Problem:
Score : 200 points

Problem Statement

Given are a positive integer N and a string S of length N consisting of lowercase English letters.

Determine whether the string is a concatenation of two copies of some string.
That is, determine whether there is a string T such that S = T + T.

Constraints

1 \leq N \leq 100

S consists of lowercase English letters.

|S| = N

Input

Input is given from Standard Input in the following format:

N
S

Output

If S is a concatenation of two copies of some string, print Yes; otherwise, print No.

Sample Input 1

6
abcabc

Sample Output 1

Yes

Let T = abc, and S = T + T.

Sample Input 2

6
abcadc

Sample Output 2

No

Sample Input 3

1
z

Sample Output 3

No

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ClassLibrary1
{
    public class ListNode
    {
        public int val;
        public ListNode next;
        public ListNode(int x) { val = x; }
    }


    public class Class1
    {

        static void Main(string[] args)
        {
            long n = Int64.Parse( Console.ReadLine());
            var s = Console.ReadLine().ToCharArray();

            if (s.Length%2 == 1)
            {
                Console.WriteLine("No");
                return;
            }
            for( long i = 0; i< s.Length%2; i++)
            {
                if (s[i] == s[s.Length + i]) continue;
                else
                {
                    Console.WriteLine("No");
                    return;
                }
            }
            Console.WriteLine("Yes");
            return;

        }

        static int rec(int[] n, int i, int j, int x)
        {
            if (i + 1 == j)
            {
                return Math.Min(n[j], x);
            }
            return rec(n, i + 1, j, n[i]) + rec(n, i, j - 1, n[j]);
        }


    }
}