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())
a = list()
b = list()
c = list()
a.append(s[0])
for i in range(1,4):
    if s[i] == a[0]:
        a.append(s[i])
    elif len(b) == 0:
        b.append(s[i])
    elif s[i] == b[0]:
        b.append(s[i])
    else:
        c.append(s[i])
if (len(a) == 2) and (len(b) == 2):
    print("Yes")
else:
    print("No")