How to stretch this equal button in flutter?

main.dart

import "package:flutter/material.dart";

class MainScreen extends StatefulWidget {
  @override
  State<MainScreen> createState() => _MainScreenState();
}

class _MainScreenState extends State<MainScreen> {
  TextEditingController input_controller = TextEditingController();
  var input_value = "";
  var operator = "";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: Container(
          padding: EdgeInsets.all(8),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: [
              Center(
                child: Container(
                  child: Image.asset("assets/images/bunny.png"),
                  height: 300,
                ),
              ),
              // SizedBox(height: 180),
              Text(
                "Kalculator",
                style: TextStyle(
                  fontSize: 60,
                  color: Colors.grey,
                  fontWeight: FontWeight.bold,
                ),
              ),
              // SizedBox(height: 80),
              TextField(
                controller: input_controller,
                cursorColor: Colors.black,
                decoration: InputDecoration(
                  focusedBorder: OutlineInputBorder(
                      borderSide: BorderSide(color: Colors.grey, width: 2)),
                  border: OutlineInputBorder(),
                ),
              ),
              Row(
                // mainAxisSize: MainAxisSize.max,
                mainAxisAlignment: MainAxisAlignment.end,
                crossAxisAlignment: CrossAxisAlignment.end,
                children: [
                  Column(
                    // ! Can't stretch button.

                    children: [
                      ElevatedButton(
                          style: ButtonStyle(
                            backgroundColor:
                                MaterialStateProperty.all(Colors.grey.shade600),
                          ),
                          child: Text(
                            "=",
                            style: TextStyle(fontSize: 26),
                          ),
                          onPressed: () {
                            setState(() {
                              if (input_controller.text.isNotEmpty) {
                                if (operator.isNotEmpty) {
                                  input_controller.text = calculate(
                                      int.parse(input_controller.text));
                                  input_value = "";
                                  operator = "";
                                }
                              }
                            });
                          }),
                    ],
                  ),
                  SizedBox(
                    width: 8,
                  ),
                  Column(
                    children: [
                      ElevatedButton(
                          style: ButtonStyle(
                            backgroundColor:
                                MaterialStateProperty.all(Colors.grey.shade600),
                          ),
                          child: Icon(Icons.add),
                          onPressed: () {
                            setState(() {
                              if (input_controller.text.isNotEmpty) {
                                input_value = input_controller.text;
                                input_controller.text = "";
                                operator = "+";
                              }
                            });
                          }),
                      ElevatedButton(
                          style: ButtonStyle(
                            backgroundColor:
                                MaterialStateProperty.all(Colors.grey.shade600),
                          ),
                          child: Icon(Icons.remove),
                          onPressed: () {
                            if (input_controller.text.isNotEmpty) {
                              input_value = input_controller.text;
                              input_controller.text = "";
                              operator = "-";
                            }
                          }),
                      ElevatedButton(
                          style: ButtonStyle(
                            backgroundColor:
                                MaterialStateProperty.all(Colors.grey.shade600),
                          ),
                          child: Icon(Icons.close),
                          onPressed: () {
                            if (input_controller.text.isNotEmpty) {
                              input_value = input_controller.text;
                              input_controller.text = "";
                              operator = "x";
                            }
                          }),
                      ElevatedButton(
                          style: ButtonStyle(
                            backgroundColor:
                                MaterialStateProperty.all(Colors.grey.shade600),
                          ),
                          child: Text(
                            "/",
                            style: TextStyle(fontSize: 26),
                          ),
                          onPressed: () {
                            if (input_controller.text.isNotEmpty) {
                              input_value = input_controller.text;
                              input_controller.text = "";
                              operator = "/";
                            }
                          }),
                    ],
                  )
                ],
              )
            ],
          ),
        ),
      ),
    );
  }

  String calculate(int num2) {
    if (input_value.isEmpty) {
      return "";
    }
    var num1 = int.parse(input_value);
    if (operator == "+") {
      return "${num1 + num2}";
    } else if (operator == "-") {
      return "${num1 - num2}";
    } else if (operator == "x") {
      return "${num1 * num2}";
    } else if (operator == "/") {
      return "${num1 ~/ num2}";
    } else {
      return "";
    }
  }
}