#include<fstream.h>
ifstream f("fact.in");
ofstream g("fact.out");
long x,p,n,nr,u,v,c;
int main(){
f>>p;
if(p==0) g<<1;
else
{
u=0;nr=0;v=1000000000;
while(u<=v)
	     {
    n=(u+v)/2;x=5;
    nr=0;
    while(n>=x)
	       {
	     nr=nr+n/x;
       x=x*5;
		}

     if(nr<p)
	u=n+1;
     else
	if (nr>p)
	    v=n-1;
	else
	   { while(n%5!=0)
	       n--;
	       break;
	       }

      }
if(u>v)
  g<<-1;
  else

   g<<n;
   }
return 0;
}