#include<fstream>
using namespace std;
ifstream f("factorial.in");
ofstream g("factorial.out");
int calc(int n)
{	int s=0,p=5;
	while(p<=n) {s=s+n/p; p*=5;}
	return s;
}
int p,m,v,nr,st=1,dr=2000000000;
int main()
{	f>>p;
	if(p==0) g<<1<<'\n';
	else
	{	bool w=1;
		while(st<=dr && w) 
		{	m=(st+dr)/2;
			v=calc(m);
			if(v==p) nr=m-m%5,w=0;
			else if(v<p) st=m+1; else dr=m-1;
		}
		if(w==0) g<<nr<<'\n'; else g<<-1<<'\n';
	}
	g.close();
	return 0;
}