#include<fstream.h>

ifstream f("fact.in");
ofstream g("fact.out");

long p;

int zero(long x)
 {
  int nr,r,z,m;
  r=5;
  nr=0;
  z=0;
  while(nr<x)
   {
    m=r;
    if(m%5==0) { nr++; m=m/5; }
    if(m%5==0) while(m%5==0)
		 {
		  nr++;
		  z++;
		  m=m/5;
		 }
    r=r+5;
   }
  if(nr>x) return -1;
  else return x-z;
 }

int main()
 {
  f>>p;
  if(p==0) g<<1;
  else if(zero(p)<0) g<<zero(p);
       else g<<5*zero(p);
  return 0;
 }