#include<fstream.h>
long p,n,m;
int main()
{
 ifstream f("fact.in");
 ofstream g("fact.out");
 f>>p;
 if (p<0) g<<"-1";
 else
 {
 n=1;
 long d=0,c=0;
 while(d<p || c<p)
  {
   m=n;
   while(m!=0 && m%2==0)
    {
     d++;
     m=m/2;
    }
    while(m!=0 && m%5==0)
    {
     c++;
     m=m/5;
    }
   if (c<p || d<p) n++;
  }
  g<<n;
 }
  g.close();
  return 0;
}