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: Runtime Error)

n = int(input())
p = list(map(int, input().split()))

ans = 0

#+2まで考慮してるから、nの数を-2にして調整しろ
for i in range(n-2):
	if p[i] < p[i + 1] < p[i + 2] or p[i + 2] < p[i + 1] < p[i]:
		ans = ans + 1

print(ans)