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 s1,s2,s3,s4;
  printf("4つの英大文字からなる文字列Sを1文字ずつ入力してください。\nS:\n");
  scanf("%s%s%s%s",&s1,&s2,&s3,&s4);
if((s1==s2)&&(s3==s4))
{
if(s2!=s3)
	printf("yes\n");
else 
    printf("no\n");
}

else if((s1==s3)&&(s2==s4))
{
if(s2!=s3)
	printf("yes\n");
else 
    printf("no\n");
}

else if((s1==s4)&&(s2==s3))
{
if(s1!=s3)
	printf("yes\n");
else 
    printf("no\n");
}


else
	printf("no\n");

return 0;
}