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: Wrong Answer)

S=str(input())
a=S[0]
if a==S[1]:
  if S[2]==S[3]:
    print("Yes")
  else:
    print("No")
    
else:
  b=S[1]
  if (a==S[2] or b==S[2]) and (a==S[3] or b==S[3]):
    print("Yes")
    
  else:
    print("No")