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(void){
  char str[5];

  scanf("%s", str);

  if(str[0]==str[1]&&str[2]==str[3]){
    printf("Yes\n");
  }else if(str[0]==str[2]&&str[1]==str[3]){
    printf("Yes\n");
  }else if(str[0]==str[3]&&str[1]==str[2]){
    printf("Yes\n");
  }else{
    printf("NO\n");
  }

  return 0;
}