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++ (GCC 9.2.1) (judge verdict: Accepted)

#include "bits/stdc++.h"

//#include <atcoder/all>

using namespace std;
//using namespace atcoder;

//#define int long long
#define ll long long

ll INF = (1LL << 60);
int mod = 998244353;
using P = pair<ll, ll>;

signed main() {
	string s; cin >> s;
	map<int, int>mp;
	for (int i = 0; i < s.size(); i++) {
		mp[s[i]]++;
	}
	bool ok = true;
	if (mp.size() == 2) {
		for (auto p : mp) {
			if (p.second != 2)ok = false;
		}
	}
	else {
		ok = false;
	}
	if (ok)cout << "Yes" << endl;
	else cout << "No" << endl;
	return 0;
}