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 (int argc, char* argv[]) {
  char s[4];
  scanf("%s", s);

  int cnt = 0;
  for (int i = 0; i < 4; i++) {
    for (int j = 0; j < 4; j++) {
      if (s[i] == s[j]) cnt++;
    }
  }

  if (cnt == 8) printf("Yes\n");
  else printf("No\n");

  return 0;
}