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 Python (3.4.3) (judge verdict: Accepted)

#!/usr/bin/env python3
import bisect
import collections
import sys

sys.setrecursionlimit(1000000)
ACMOD = 1000000007
INF = 1 << 62


YES = "Yes"  # type: str
NO = "No"  # type: str


def solve(S: str):
    c= collections.Counter(S)
    if c.most_common()[0][1] == 2 and c.most_common()[1][1] == 2:
        print("Yes")
    else:
        print("No")

def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = next(tokens)  # type: str
    solve(S)

if __name__ == '__main__':
    main()