#include<fstream>
#include<limits>
using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");
int ok;
long long k, m, i, j, x, p;
int main()
{
	f>>p;
	i=1;
	j=LONG_MAX;
	ok=0;
	while(i<=j&&ok==0)
	{
		m=(i+j)/2;
		x=5;
		k=0;
		while(x<=m)
		{
			k=k+m/x;
			x=x*5;
		}
		if(k==p)ok=1;
		else if(k>p)j=m-1;
		else i=m+1;
	}
	if(ok==0) g<<-1;
	else{
		while(m%5!=0)m--;
		g<<m;
	}
	f.close();
	g.close();
	return 0;
}