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");

	}



}