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: Accepted)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int comp(const void *a, const void *b)
{
	return *(char*)a - *(char*)b;
}

int main(void){
	
	char str[5];
	
	fgets(str,sizeof(str),stdin);
//	printf("%s\n",str);
	
	qsort(str,4,sizeof(char),comp);
	
//	printf("%s\n",str);
	
	if(str[0] == str[1] && str[2] == str[3] && str[0] != str[2])
		printf("Yes");
	else
		printf("No");
	
	return 0;
}