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 s[5];
	scanf("%s", s);
	char c;
	int i;
	for (i = 0; i < 3; i++)
	{
		if (s[i] > s[i + 1])
		{
			c = s[i];
			s[i] = s[i + 1];
			s[i + 1] = c;
			if (i > 0)
				i -= 2;
		}
	}
	if (s[0] == s[1] && s[2] == s[3] && s[1] != s[2])
		printf("Yes\n");
	else
		printf("No\n");
	return 0;
}