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)

a=input()
s = {a[0],a[1],a[2],a[3]}
if len(s) == 2:
  b = s.pop()
  flag1 = a.count(b)
  c = s.pop()
  flag2 = a.count(c)
  if flag1 ==2 and flag2 == 2:
    print("Yes")
  else:
    print("No")
else:
  print("No")