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 <iomanip>
#include <string>
#include <vector>
#include <cmath>
#include <algorithm>
using namespace std;

int main() {
	string str;
	cin >> str;
	bool check = false;

	if (str[0] == str[1] && str[2] == str[3] && str[0] != str[2]) {
		check = true;
	}
	else if (str[0] == str[2] && str[1] == str[3] && str[0] != str[1]) {
		check = true;
	}
	else if (str[0] == str[3] && str[1] == str[2] && str[0] != str[1]) {
		check = true;
	}

	if (check) {
		cout << "Yes" << endl;
	}
	else {
		cout << "No" << endl;
	}
}