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 (4.10.0) (judge verdict: Accepted)

let () =
  let rec charlist_of_string str n i =
    if i = n then [] else str.[i] :: charlist_of_string str n (i+1) in
  Scanf.scanf "%d\n%s\n" @@ fun n s ->
  let former = charlist_of_string (String.sub s 0 (n/2)) (n/2) 0 in
  let later = charlist_of_string (String.sub s (n/2) (n/2)) (n/2) 0 in
  let ans = List.fold_left2
      (fun ans x y -> if x=y then ans && true else false) true former later in
  Printf.printf "%s\n" (if ans && n mod 2 = 0 then "Yes" else "No")