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           Control.Applicative()
import           Data.List

main :: IO ()
main = do
    s <- getLine
    let t = sort s
    putStrLn $ if t !! 0 == t !! 1 && t !! 2 == t !! 3 && t !! 1 /= t !! 2
        then "Yes"
        else "No"