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>

int main()
{
	char str[3];
	int k;
	gets(str);
		if (str[0] == str[1]) 
		{
			if (str[2] == str[3] && str[0] != str[2]) 
			{
				printf("Yes");
			}
			else 
			{
				printf("No");
			}
		}
		else if (str[0] == str[2])
		{
			if (str[1] == str[3] && str[0] != str[1])
			{
				printf("Yes");
			}
			else
			{
				printf("No");
			}
		}
		else if (str[0] == str[3])
		{
			if (str[1] == str[2] && str[0] != str[1])
			{
				printf("Yes");
			}
			else
			{
				printf("No");
			}
		}
		else
		{
			printf("No");
		}

	return 0;
}