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[5];
	char s,s2;
	int cou=0,cou2=0,flag=0;;
	scanf("%s",S);
	s=S[0];
	for(int i=0;i<4;i++){
		if(s!=S[i] && flag==0){
			s2=S[i];
			flag++;
		}
		if(s==S[i])cou++;
		else if(s2==S[i])cou2++;
	}

	if(cou==2 && cou2 ==2)printf("Yes\n");
	else printf("No\n");
	return 0;
}