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: Accepted)

using System;
using System.Text;
using System.Collections.Generic;
using System.Linq;
using E = System.Linq.Enumerable;
 
class Program
 {

        static void Main(string[] args)
        {
          //入力を受け取る
          var N = int.Parse(Console.ReadLine());
          string S = Console.ReadLine();
          //var A = Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToArray();
          var front = S.Substring(0, N/2);
          var back =  S.Substring(N/2, N/2);
          
          if(N%2 == 0 && front == back){
            Console.WriteLine("Yes");
          }else{
            Console.WriteLine("No");
          }
        }
  
        // 最小公倍数
        public static long Lcm(long a, long b) {
            return a * (b / Gcd(a, b));
        }

        // ユークリッドの互除法 
        public static long Gcd(long a, long b) {
            if (a < b)
                // 引数を入替えて自分を呼び出す
                return Gcd(b, a);
            while (b != 0) {
                var remainder = a % b;
                a = b;
                b = remainder;
            }
            return a;
        }
  
}