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 = input()

ch1 = ''
ch2 = ''
ct1 = 0
ct2 = 0
for c in s:
	if ch1 == '':
		ch1 = c
		ct1 += 1
	elif ch1 == c:
		ct1 += 1
	elif ch2 == '':
		ch2 = c
		ct2 += 1
	elif ch2 == c:
		ct2 += 1

if ct1 == 2 and ct2 == 2:
	print('Yes')
else:
	print('No')