#include<fstream>
#include<iostream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{
	long long p,n=0,k1,k2,z=25;
	register long long i=0;
	fin>>p;
	if(p==0)
		fout<<1;
	n=p*5;
	k1=n;
	while(z<k1)
	{
		i++;
		z=z*5;
		k1=k1-i*5;
	}
	n=(p+1)*5;
	k2=n;
	z=25;
	i=0;
	while(z<k2)
	{
		i++;
		z=z*5;
		k2=k2-i*5;
	}
	if(k2<=k1)
		fout<<-1;
	else
		fout<<k1;
	return 0;
}