#include <fstream.h>
long p,l,u,m,nr,c;
ifstream f("fact.in");
ofstream g("fact.out");
int main(){
f>>p;

l=1;u=200;
while (l<=u){
	m=(l+u)/2;
	nr=0;c=1;
	while (m>=c){
		c=c*5;
		nr+=m/c;
		}
	if (nr==p){
	     c=1;       nr=0;

	     while ((m-1)>=c)
	     {  c=c*5;
		 nr+=(m-1)/c;  }
		break;}
	else if (nr>p)
		u=m-1;
		else l=m+1;
	}
if (l<=u)
	g<<m;
else g<<-1;

return 0;}