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())
adic = {}

for i in range(4):
  if not s[i] in adic:
    adic[s[i]] = 1
  else:
    adic[s[i]] += 1
    
abool = True
if len(adic) == 2:
  for item in adic:
    if adic.get(item) != 2:
      abool = False
else:
  abool = False
  
if abool:
  print('Yes')
else:
  print('No')