Problem

prog.java

/* package codechef; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Codechef
{
	public static void main (String[] args) throws java.lang.Exception
	{
	 Scanner scanner = new Scanner(System.in);
    int size = scanner.nextInt();
    String input[] = new String[size];
    for (int i = 0; i < size; i++) {
      input[i] = scanner.next();
    }
    sortArray(input);
     StringBuilder builder = new StringBuilder();
    for (int i = 0; i < size; i++) {
      builder.append(input[i]);
    }
    System.out.println(builder.toString());
	}
	
	public static void sortArray(String[] input) {
    for (int i = 0; i < input.length; i++) {
      for (int j = 0; j < input.length - i-1; j++) {
        if (isLarge(input[j], input[j + 1])) {
          String temp = input[j];
          input[j] = input[j + 1];
          input[j + 1] = temp;
        }
      }
    }
  }

  public static boolean isLarge(String s1, String s2) {
    return s1.compareTo(s2) < 0;
  }
}