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>
#include <stdlib.h>
int compare_int(const void *a, const void *b)
{
    return *(int*)a - *(int*)b;
}
int main(void) {
  char s[4];
  int r;
  scanf("%s",s);
  r = s[0] == s[1] && s[2] == s[3];
  r =  r || s[0] == s[2] && s[1] == s[3];
  r = r || s[0] == s[3] && s[1] == s[2];
  if(r) {
    puts("Yes");
  } else {
    puts("No");
  }
  return 0;
}