#include<stdio.h>

long nrz(long c )
{
  long t=0;
  while(c)
  {
    t+=c/5;
    c/=5;
  }
  return t;
}
int main()
{
  freopen("fact.in","r",stdin);
  freopen("fact.out","w",stdout);
  long p;
  scanf("%ld",&p);
  long li,lf,m;
  li=(p+1)/2;
  lf=p;
  while(li<=lf)
  {
    m=(li+lf)/2;
    if(nrz(5*m)==p) break;
    if(nrz(5*m)>p) lf=m-1;
      else li=m+1;
  }
  if(li<=lf) printf("%ld",5*m);
     else printf("-1\n");
  /*m=5;
  printf("%ld",nrz(5*m));*/
  return 0;
}