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>
int main()
{
	char a[4],s='\0',k='\0';
	gets(a);
	s=a[0];
	for(int i=1;i<4;i++)
	{
		if(a[i]!=s && k=='\0')  
			k=a[i];
		else if(a[i]!=s && a[i]!=k)
		{
			printf("No");
			return 0;
		} 
			 		
	} 
	if(k=='\0')
	{
		printf("No");
	}
		
	else
	{
		printf("Yes");
	}	
		
}