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]
b = S[1]
c = S[2]
d = S[3]
if a == b and c ==d:
  print('Yes')
elif a == c and b == d:
  print('Yes')
elif a == d and b == c:
  print('Yes')
else:
  print('No')