Help me in solving LAPIN problem

help
,
1

My issue

My code

/* 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
	{
		// your code goes here
		Scanner sc=new Scanner(System.in);
		String str,st1,st2;char ch;int i,j,n,sum,mid;
		n=sc.nextInt();
		for(i=0;i<n;i++)
		{
		    str=sc.nextLine();
		    sum=str.length();
		    mid=sum/2;
		    st1=str.substring(0,mid);
		    st2=str.substring(mid);
		    if(st1.equalsIgnoreCase(st2))
		    System.out.println("YES");
		    else
		    System.out.println("NO");
		}
	}
}

Problem Link: LAPIN Problem - CodeChef