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: Runtime Error)

#include <stdio.h>
int main(void){
  char s[128];
  if(scanf("%s",s) == 1){};
  if(s[0] == 0 || s[1]  == 0 || s[2] == 0|| s[3] ==0){puts("No");return 1;}
  if((s[0] == s[1] && s[0] == s[1]) && (s[0] == s[2] && s[0] == s[3])) {puts("No");return 1;}
if( (s[0] == s[1] && s[2] == s[3]) || (s[0] == s[2] && s[1] == s[3]) || (s[0] == s[3] && s[2] == s[1])){
   puts("Yes");
  }else{
   puts("No");
}
return 0;
}