#include<iostream>
#include<fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int main()
{ long long p,n,t=5,x=0;
  f>>p;
  n=p*5;
  if(p==0)
  g<<1;
  else
  {
  while(t<=n)
  {
   t=t*5;
   x++;
   if(t<=n)
   n-=5*x;
  }
  g<<n;
  }
  f.close();
  g.close();
  return 0;
}