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 (Clang 3.8.0) (judge verdict: Accepted)

#include<stdio.h>
int main(void) {
	char s[5];
	int c[4] = {0,0,0,0};
	scanf("%s", s);
	for (int i = 0; i < 5; i++) {
		for (int j = 0; j < 5; j++) {
			if (s[i] == s[j] && i!=j) {
				c[i]++;
			}
		}
	}
	if (c[0] == 1 && c[1] == 1 && c[2] == 1 && c[3] == 1) {
		printf("Yes\n");
	}
	else {
		printf("No\n");
	}

	return 0;
}