#include<fstream>
using namespace std;
int zero(int x)
{
	int putere=1;
	int z=0;
	while(x>=putere)
	{
		putere=putere*5;
		z=z+x/putere;
	}
	return z;
}
ifstream f("fact.in");
ofstream g("fact.out");
int i,p,st,dr,m;
int main()
{
	f>>p;st=1;dr=5*p;
	while(st<=dr)
	{
		m=(st+dr)/2;
		if(p<=zero(m))
			dr=m-1;
		else
			st=m+1;
	}
	if(zero(st)==p)
		g<<st;
	else g<<"-1";
		return 0;
}