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(void)
{
	char S[5];
	scanf("%s", S);

	int i;
	int alp[26] = {0};
	for (i = 0; i < 4; i++) {
		int idx = S[i] - 'A';
		alp[idx]++;
	}

	int cnt = 0;
	for (i = 0; i < 26; i++)
		if (alp[i] == 2)
			cnt++;

	puts(cnt == 2 ? "Yes" : "No");
	return 0;
}