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 OCaml (4.02.3) (judge verdict: Accepted)

open Batteries
(* 前からst文字を消す *)
let cut st str = String.init (String.length str - st) (fun a -> String.get str (a+st))
(* 後ろからed文字を消す *)
let back_cut ed str = String.init (String.length str - ed) (String.get str)
let n = read_int ()
let s = read_line ()
let l = String.length s / 2
let _ = 
  (if n mod 2 = 1 then "No" else
  if cut l s = back_cut l s then "Yes" else "No") |> print_endline