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[4];
  char a;
  int f = 0;
  scanf("%s", str);
  for (int i = 0; i < 4; i++) {
    a = str[i];
    for (int j = 0; j < 4; j++) {
      if (a == str[j]) {
        f++;
      }
    }
  }
  if (f >= 8) {
    printf("Yes\n");
  } else {
    printf("No\n");
  }
  return 0;
}