#include<stdio.h>
using namespace std;
int i,p,u,nr,m,pi;
int nrzer(int n)
{
	int p1=1;
	int s=0;	
	for(i=1;i<=30;i++)
	{
		p1=p1*5;
		if(p1>n) break;
		s=s+n/p1;
	}
	return s;
}
int main()
{
freopen("fact.in","r",stdin);
freopen("fact.out","w",stdout);
scanf("%d",&pi);
p=1;
u=5*pi+5;
while(p<=u)
{
	m=(p+u)/2;
	nr=nrzer(m);
	if(nr>pi) u=m-1;
	else
	if(nr<pi) p=m+1;
	else break;
}
if(p<=u) printf("%d",m-m%5);
else printf("-1");
return 0;
}