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);

	if ((s[0] == s[1] && s[2] == s[3])||
		(s[0] == s[2] && s[1] == s[3])||
		(s[0] == s[3] && s[1] == s[2])) {
		if ((s[0] == s[1]) && (s[1] == s[2]) && (s[2] == s[3])) {
			printf("No");
		}
		else {
			printf("Yes");
		}
	}
	else {
		printf("No");
	}
	getchar();

	getchar();

	return 0;
}