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(void){
  char s[4];
  scanf("%s", s);
  if(s[0] == s[1]){
    int count = 0;
    if(s[0] == s[2]) count ++;
    if(s[0] == s[3]) count ++;
    if(count == 0 && s[2] == s[3]){
      printf("Yes");
    }else{
      printf("No");
    }
  }else{
    int count1 = 0;
    int count2 = 0;
    if(s[0] == s[2]) count1 ++;
    if(s[0] == s[3]) count1 ++;
    if(s[1] == s[2]) count2 ++;
    if(s[1] == s[3]) count2 ++;
    if(count1 == 1 && count2 == 1){
      printf("Yes");
    }else{
      printf("No");
    }
  }
  return 0;
}