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 = input()

if not sum(list(map(lambda x: x == S[0], S))) == 2:
  print('No')
else:
  s = S[1:]
  idx = s.index(S[0])

  if idx == 0:
    if s[1] == s[2]:
      print('Yes')
    else:
      print('No')
  elif idx == 1:
    if s[1] == s[2]:
      print('Yes')
    else:
      print('No')
  elif idx == 2:
    if s[1] == s[0]:
      print('Yes')
    else:
      print('No')