#include<fstream.h>
unsigned long st,dr,p,x,m,n;
unsigned long check(unsigned long x)
	{
	unsigned long s=0,q=5;
	while(q<=x)
		{
		s+=x/q;
		q*=5;
		}
	return s;
	}
int main()
{
ifstream f("fact.in");
ofstream g("fact.out");
f>>p;
st=5;
dr=4200000000;
if(p==0)g<<1;
else 
{while(1)
	{
	m=(st+dr)>>1;
	x=check(m);
	if(x<p)if(st!=m)st=m;
		else {n=0;break;}
	else if(x>p)dr=m;
	else {n=m;break;}
	}
if(n>0)g<<(n-n%5);
else g<<"-1";}
return 0;
}