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: Wrong Answer)

#include<stdio.h>
int main(){
  char str[5];
  int i,j,c1,c2 = -1,cn1 = 0,cn2 = 0;
  for(i = 1, c1 = str[0],cn1++;i < 5 - 1;i++){
    if(c1 == (int)str[i]){
      cn1++;
    }else{
      if(c2 == -1){
        c2 = (int)str[i];
        cn2++;
      }else{
        break;
      }
    }
  }
  if(cn1 == cn2 && cn2 == 2){
    printf("Yes");
  }else{
    printf("No");
  }
  return 0;
}