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)

# Python3 (3.4.3)
import sys
input = sys.stdin.readline

# -------------------------------------------------------------
# function
# -------------------------------------------------------------


# -------------------------------------------------------------
# main
# -------------------------------------------------------------
S = list(input().rstrip())

S.sort()
print("Yes" if S[0]==S[1] and S[2]==S[3] and S[0]!=S[-1] else "No")