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 (Clang 3.8.0) (judge verdict: Accepted)

#include <stdio.h>
int main(){
  char S[5];
  int i,k;
  int num = 0;
  scanf("%s",S);
  for(i=0;i<=3;i++){
    for(k=0;k<=3;k++){
      if(S[i] == S[k]){
        num = num+1;
      }
    }
  }
  if(num == 8)printf("Yes");
  else printf("No");
}