백준 2839

백준 2839

#include<iostream>
using namespace std;

int main()
{
    int n;
    cin >> n;
    int a, b;
    a = n / 5;
    int cnt=0;
    while (1)
    {
        if (a < 0)
        {
            cout << "-1";
            return 0;
        }

        if ((n % 5 +cnt) % 3 == 0)
        {
            b = (n % 5 +cnt) / 3;
            break;
        }
        a--;
        cnt+=5;
    }
    cout << a + b;
}