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>
using namespace std;

int main() {
	char s[4]; 
	int ans = 0;
	for (int i = 0; i < 4; i++) {
		cin >> s[i];
	}

	for (int i = 0; i < 4; i++) {
		for (int j = i+1; j < 4; j++) {
			if (s[i] == s[j]) {
				ans++;
			}
		}
	}
	if (ans == 2) cout << "Yes" << endl;
	else cout << "No" << endl;

	return 0;
}