#include <fstream>


int main ()
{long p,lim,s,i,x,m;
ifstream f("fact.in");
ofstream g("fact.out");
f>>p;
lim=p-(p%250000);
s=lim;

if (lim%500000==0) x=(4*lim+5)/5;
else x=(4*lim+10)/5;

if(lim==0) x=0;
if(p==0) g<<1;
else
for (i=lim*5+5;i<=p*5;i=i+5)
	{m=i;
	while (m%5==0)
		{if(m==0) break;
		m=m/5;
		s=s+1;
		if (m==1) break;
		}
	if (m!=0) x=x+1;
	if (s==p) {g<<x*5; break;}
	else if (s>p) {g<<-1; break;}
	}
if(p%250000==0) g<<x*5;
return 0;
}