#include<fstream.h>
#include<math.h>
long long p,mij,inc,sf,gasit,p2,t;
int main()
{
ifstream in("fact.in");
ofstream out("fact.out");
in>>p;
inc=5;
sf=5*p;
gasit=0;

while((gasit==0)&&(inc<=sf))
{ mij=(inc+sf)/2;
   t=1;
   p2=0;
   while(t<=mij)
   {t=t*5;
    p2=p2+int(mij/t);
    }
   if(p2==p) gasit=1;
   if(p2>p) sf=mij-1;
   if(p2<p) inc=mij+1;
}
if(gasit==1) if(mij%5==0) out<<mij;
		     else {while(mij%5!=0)
			  mij=mij-1;
			  out<<mij;
                          }
          else out<<"-1";
in.close();
out.close();
return 0;
}