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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>
#include <string>
#include <vector>
int main()
{
	std::string s;

	std::cin >> s;

	std::string YesNo = "Yes";
	int count;
	int count2 = 0;
	for(int i=0; i<3; i++){
		count = 0;
		for (int j = i+1; j < 4; j++) {
			if (s[i] == s[j])
				count++;
			if (count > 1)
				YesNo = "No";
		}
		if (count == 1)
			count2++;
	}

	if (count2 != 2)
		YesNo = "No";

	std::cout << YesNo << std::endl;
		
	return 0;
}