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<set>
#include<vector>
#include<utility>
#include<algorithm>

using namespace std;

#define LL long long



int main() {
	string S;
	cin >> S;
	char a = S[0], b = S[1];
	if (a == b) {
		b = S[2];
		if (a != b && b == S[3])
			cout << "Yes" << endl;
		else cout << "No" << endl;
	}
	else {
		if ((a == S[2] || a == S[3]) && (b == S[2] || b == S[3])) {
			cout << "Yes" << endl;
		}
		else cout << "No" << endl;
	}
	return 0;
}