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 8.8.3) (judge verdict: Wrong Answer)

main = do
  s <- getLine
  let a:b:c:d:[] = s
  putStrLn $
    if a /= b || a /= c || a /= d && (
       a == b && c == d ||
       a == c && b == d ||
       a == d && b == c ) then
      "Yes"
    else
      "No"