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>
using namespace std;
using ll = long long;
using P = pair<ll, ll>;
#define rep(i, n); for(ll i = 0; i < (ll)n; i++)

int main() {
  map<char,int> mp;
  rep(i,4){
    char s; cin >> s;
    auto itr = mp.find(s);        // "s" が設定されているか？
    if( itr != mp.end() )
      mp[s]++;
    else
      mp[s] = 1;
  }
  
  bool ok = true;
  for(auto it = mp.begin(); it!=mp.end(); it++){
    if(it->second != 2)
      ok = false;
    //cout << it->second << endl;
  }
  if(mp.size() != 2)
    ok = false;
  //cout << mp.size() << endl;
  
  if(ok)  cout << "Yes" << endl;
  else  cout << "No" << endl;
}