#include<fstream.h>
unsigned long  a=0,b=500000000,aux,s,m,h,p;
int main()
{ifstream f("fact.in");ofstream g("fact.out");
f>>p;
while(s==0 && b>=a)
{m=(a+b)/2;aux=m;h=0;
while(aux!=0)
{h=h+aux/5;aux=aux/5;}

if(h==p && m%5!=0)
while(m%5!=0) m--;
if(h==p && m%5==0)
 s=1;
  if(h>p) b=m-5;
if(h<p)      a=m+5;}
if(s==0) g<<"-1";
else g<<m;
return 0;}