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>
#include<stdlib.h>

char S[10];

int comp(const void* a, const void* b){
	if(*(char*)a-*(char*)b>0){
    	return 1;
    }else if(*(char*)a-*(char*)b == 0){
    	return 0;
    }else{
    	return -1;
    }
}

int main(void){
  	scanf("%4s", S);
  	qsort(S, 4, sizeof(char), comp);
  	if(S[0]==S[1] && S[2]==S[3]){
    	printf("Yes");
    }else{
    	printf("No");
    }
  	return 0;
}