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: Wrong Answer)

#include <iostream>
#include <string>
#include <cmath>
#include <vector>
#include <algorithm>
#include <functional>
#include <array>

using namespace std;


int main(void)
{
	string s;
	cin >> s;

	char a, b;
	int count_a;


	
	if ((s[0] == s[1]) && (s[2] == s[3])) {
		cout << "Yes" << endl;
		return 0;
	}
	else if((s[0] == s[2]) && (s[1] == s[3])) {
		cout << "Yes" << endl;
		return 0;
	} if ((s[0] == s[3]) && (s[1] == s[2])) {
		cout << "Yes" << endl;
		return 0;
	}
	cout << "No" << endl;

	return 0;
}