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 (3.8.2) (judge verdict: Accepted)

s=input()
a=0
b=0
c=0
for i in range(1,4):
  if ord(s[0])==ord(s[i]):
    a=i
    b+=1
if b==1:
  if a==1:
    if ord(s[2])==ord(s[3]):
      print('Yes')
    else:
      print('No')
  elif a==2:
    if ord(s[1])==ord(s[3]):
      print('Yes')
    else:
      print('No')
  elif a==3:
    if ord(s[1])==ord(s[2]):
      print('Yes')
    else:
      print('No')
else:
    print('No')