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 compare(const void *a, const void *b) {
	char x = *(char *)a;
	char y = *(char *)b;
	if(x == y) {
		return 0;
	} else if(x > y) {
		return -1;
	} else {
		return 1;
	}
}

int main() {
	char input[5];

	scanf("%s", &input);

	qsort(input, 5, sizeof(char),compare);

	if(input[0] == input[1] && input[2] == input[3]) {
		printf("Yes\n");
	} else {
		printf("No\n");
	}

	return 0;
}