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 C (GCC 5.4.1) (judge verdict: Accepted)

    #include<stdio.h>
    int main(void)
    {
      char s[4];
      int i,j;
      int count=0;
      scanf ("%s",&s);
      for(i=0;i<4;i++){
        for (j=0;j<4;j++){
          if(s[i]==s[j]){
            count++;
          }
        }
      }
      if (count != 8){
        printf("No\n");
      }
      else{
        printf("Yes\n");
      }
      return 0;
    }