Main.java

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
		String file = "file.txt";
		String str = "3";
		double r = Double.parseDouble(str);
		
		try{
			PrintWriter pw = new PrintWriter(
				new BufferedWriter(new FileWriter(file)));
			pw.println(r);
			pw.close();
		}catch(IOException e){
		}
    }
}