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];
	char count = 0;
	
	gets(s);
	for(char i = 0; i < 3; i++)
	{
		for(char j = i + 1; j < 4; j++) if(s[i] == s[j]) count++;
	}
	if(count == 2) printf("Yes"); else printf("No");
}