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 a[4];
  
  scanf("%s",a);
  int i,j;
  int k,l;
  k=0;
  l=0;
  if(a[0]==a[1]){
  	if(a[1]!=a[2]){
        if(a[2]==a[3]){
          printf("Yes");
          k+=1;
        }
    }
  }
  if(a[0]==a[3]){
    if(a[0]!=a[1]){
      if(a[1]==a[2]){
        printf("Yes");
          k+=1;
      }
    }
  }
  if(a[0]==a[2]){
      if(a[0]!=a[1]){
        if(a[1]==a[3]){
          printf("Yes");
            k+=1;
        }
      }
    }
  if(k==0){
            printf("No");
  }
  return 0;
}