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>
int cmp(const void *a,const void *b)
{
	return *(char *)a - *(char *)b;
}
int main(void)
{
	char ch[4];
	scanf("%s",ch);
	int n = 4;
	int i;
	int flag = 1;
	qsort(ch,n,sizeof(ch[0]),cmp);
	for(i = 0;i<4;i+=2)
	{
		if(ch[i] != ch[i+1])
		{
				flag = 0;
				break;
		}
	}
	printf(flag == 1?"Yes":"No");
	return 0;
}