#include<iostream>
#include<fstream>
using namespace std;
long p,n,k;

long putere(long nr)
{
	int k=0;
	while(nr%5==0)
	{
		++k;
		nr/=5;
	}
	return k;
}

int main()
{
	ifstream f("fact.in");
	ofstream g("fact.out");
	f>>p;
	n=0;
	k=0;
	do
	{
		n+=5;
		k=k+putere(n);
	}while(k<p);

	if(p==0) g<<1;
	 else 
		 if(k!=p) g<<-1;
			else g<<n;
}