Problem:
Score : 100 points

Problem Statement

You are given a 4-character string S consisting of uppercase English letters.
Determine if S consists of exactly two kinds of characters which both appear twice in S.

Constraints

The length of S is 4.

S consists of uppercase English letters.

Input

Input is given from Standard Input in the following format:

S

Output

If S consists of exactly two kinds of characters which both appear twice in S, print Yes; otherwise, print No.

Sample Input 1

ASSA

Sample Output 1

Yes

S consists of A and S which both appear twice in S.

Sample Input 2

STOP

Sample Output 2

No

Sample Input 3

FFEE

Sample Output 3

Yes

Sample Input 4

FREE

Sample Output 4

No

Solution in Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Data.List
import Text.Printf

main :: IO()
main = do
  input <- getLine
  let ans = slv input
  printf "%s" ans

slv :: String -> String
slv str | res == 2 = "Yes"
        | otherwise = "No" 
  where res = length $ group $ sort str