[AtCoder]ABC042A 和風いろはちゃんイージー ~ 43[C++]

#include <bits/stdc++.h>
using namespace std;
 
int main() {
  string a, b, c;
    cin >> a >> b >> c;
    string n = a + b + c;
  if (count(n.begin(), n.end(), '5') == 2  && count(n.begin(), n.end(), '7') == 1){
    cout << "YES" << endl;
  }
  else {
    cout << "NO" << endl;
  }
}

#include <bits/stdc++.h>
using namespace std;
 
int main() {
  int children;
    cin >> children;
  int candies = 0;
  candies = (1 + children)*children/ 2;
  
  cout << candies << endl;
}