#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int mult,n,ptr=25,ccptr,cptr=25,ctr=1;
double m5;
int main()
{
   f >> n;
   if (n==0)
      g << 1;
   else {
   mult=5*n;
   ccptr=cptr;
   while (ptr<mult) {
    while (cptr<=mult) {
        mult-=5*ctr;
        cptr+=ccptr;
    }
    ptr*=5;
    cptr=ptr;

    ctr++;
   }
   g << mult;
   }

    return 0;
}