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: Wrong Answer)

let explode s =
  let rec exp i l =
    if i < 0 then l else exp (i - 1) (s.[i] :: l) in
  exp (String.length s - 1) []
    
let rec take n l =
  match l with
    [] -> []
  | x :: xs ->
    if n = 0 then
      []
    else x :: take (n - 1) xs

let rec drop n l =
  match l with
    [] -> []
  | x :: xs ->
    if n = 0 then
      l
    else drop (n - 1) xs 

let () =
  let n = Scanf.sscanf (input_line stdin) "%d" (fun a -> a) in
  let s = Scanf.sscanf (input_line stdin) "%s" (fun a -> a) in
  let judge cs =
    let mae = take (n/2) cs in
    let ushiro = drop (n/2) cs in
    List.for_all2 (fun a b -> a = b) mae ushiro in
  let ans = if n mod 2 = 1 then "No" else if judge (explode s) then "Yes" else "no"
  in
  print_string ans;
  print_newline ()