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;
	int similarCount = 0;
	int differentCount = 0;
	char s[5];

	scanf("%s", s);

	for (i = 0; i < 4; i++) {
		//文字列の最初の文字と同じ文字がいくつあるかカウントする
		if (s[0] == s[i]) {
				similarCount++;
		}
		//文字列の最初の文字と異なる文字がいくつあるかカウントする
		else {
			differentCount++;
		}
	}

	if (similarCount == 2 && differentCount == 2) {
		printf("Yes\n");
	}
	else {
		printf("No\n");
	}

	return 0;
}