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 Haskell (GHC 7.10.3) (judge verdict: Wrong Answer)

import Control.Applicative

isSubstr :: String -> String -> Bool
isSubstr _ [] = False
isSubstr s s'
    | m /= 0	   = isSubstr s (drop 1 s')
	| s'_repl == s = True
    | otherwise    = isSubstr s (drop 1 s')
    where m = length s `mod` length s'
    	  d = length s `div` length s'
          s'_repl = concat $ replicate d s'
          
main :: IO ()
main = do
  	s <- getLine
	print $ if isSubstr s (drop 1 s) then "Yes" else "No"