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>
int main(void)
{
	int i, j, k;
	int count = 0;
	char s[5];

	scanf("%s", s);

	for (i = 0; i < 4; i++)
	{
		if (s[i] == s[i + 1])
			count = count + 1;
	}

	for (j = 1;j < 4;j++)
	{
		if (s[j] == s[j + 1])
			count = count + 1;
	}

	for (k=2; k< 4; k++)
	{
		if (s[k] == s[k + 1])
			count = count + 1;
	}
	printf("%d", count);

	return 0;
}