#include<bits/stdc++.h>
using namespace std;
int main(){
	int a,b,c;
	cin>>a;
	if(a==4||a==7)
	{
		cout<<"-1";
		return 0;
	}
	b=a/5;
	c=a%5;
	if(c%3==0)
	c=c/3;
	else
	c=c/3+1;
	cout<<b+c;
	
	return 0;
}