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 = list(input())

dict = {}

for c in s:
    if(c in dict.keys()):
        dict[c] += 1
    else:
        dict[c] = 1

# print(dict)

result = 'Yes'

if(len(dict) != 2):
    result = 'No'

for v in dict.values():
    if(v != 2):
        result = 'No'

print(result)