#include<iostream>

using namespace std;

int main(void)
{
int input,a;
int quo, rem, one, two, three, four = 0;
cin >> input;
quo = input / 5;
    rem = input % 5;
if (quo > 0)
{
if (rem == 0)
{
cout << quo << endl;
}
else if (rem == 1)
{
one = quo + 1;
cout << one << endl;
}
else if (rem == 2)
{
a = input - 12;
if (a >= 0)
{
two = quo + 2;
cout << two << endl;
}
else
{
cout << -1 << endl;
}
}
else if (rem == 3)
{
three = quo + 1;
cout  << three << endl;
}
else if (rem == 4)
{
four = quo + 2;
cout << four << endl;
}
}
else
{
cout  << -1 << endl;
}
return 0;
}

뭐가 문제일까요??