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(){
  char s[4];
  int b[100]={};
  for(int i=0;i<4;i++){
    scanf("%c",&s[i]);
  }
  
  int cast;
  for(int i=0;i<4;i++){
    cast = s[i];
    b[cast] += 1;
  }
  int count = 0;
  for(int i=65;i<91;i++){
    if(b[i] == 2){
      count += 1;
    }
  }
  if(count == 2){
    printf("Yes\n");
  }else{
    printf("No\n");
  }
  return 0;
}