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>
#include <stdlib.h>
#define max(a, b) ((a) > (b) ? (a) : (b))
#define min(a, b) ((a) > (b) ? (b) : (a))

int asc(const void *a, const void *b){
  return *(int *)a - *(int *)b;
}

int
main(int argc, char *argv[])
{
  char s[5];
  scanf("%s", s);

  int c[10000] = {};
  
  for(int i = 0; i < 4; i++){
    c[s[i]]++;
  }
  int cnt = 0;
  for(int i = 'A'; i <= 'Z'; i++){
    if(c[i] > 0) cnt++;
  }

  if(cnt == 2) printf("Yes\n");
  else printf("No\n");

  return 0;
}