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)

s = str(input())
if s[0] == s[1]:
  if s[2] == s[3] and s[0] != s[2]:
    print("Yes")
  else:
    print("No")
elif s[0] == s[2]:
  if s[1] == s[3] and s[0] != s[1]:
    print("Yes")
  else:
    print("No")
elif s[0] == s[3]:
  if s[1] == s[2] and s[0] != s[1]:
    print("Yes")
  else:
    print("No")
else:
  print("No")