#include <fstream.h>



long fact(long p)
{long lim=p-(p%250000),s=lim,i,x,m,sol;

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

if(lim==0) x=0;
if(p==0) sol=-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) {sol=x*5; break;}
	else if (s>p) {sol=-1; break;}
	}
if(p%250000==0) sol=x*5;
return sol;
}
int main ()
{long p;
ifstream f("fact.in");
ofstream g("fact.out");
f>>p;
g<<fact(p);
return 0;
}