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()
{
	char S[4];
	int i, j, ans=0;
	for(i = 0; i < 4; ++i){
	scanf("%c", &S[i]);
	}
	for(i = 0; i < 4; ++i) {
		for(j = 0; j < 4; ++j) {			
		if(S[i] == S[j]) {
				ans +=1;
			}
		}
	}
	if(ans == 8) {
		printf("Yes");
	}
	else printf("No");
	return 0;
}