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)

let scan_int () = Scanf.scanf " %d" (fun x -> x)
let scan_string () = Scanf.scanf " %s" (fun x -> x)

let rec judge s i h =
  if i = h then true
  else if s.[i] = s.[i+h] then judge s (i+1) h
  else false

let () =
  let n = scan_int() in
  let s = scan_string() in
  if n mod 2 = 0 && judge s 0 (n/2) then Printf.printf "Yes\n"
  else Printf.printf "No\n"