#include <iostream>
#include <fstream>
using namespace std;

unsigned long fact(long nrd)
{
    unsigned long number = 1, nr = 0, first, second;
    do{
        nr++;
        first = (number % 10000) * nr;
        second = (((number / 10000) * nr) % 10000);
        number = second * 10000 + first;
        while ((number % 10) == 0) {
            number /= 10;
            nrd--;
        }
    } while (nrd);
    return nr;
}

int main()
{
    long nrd;
    fstream in, out;
    in.open("fact.in", ios_base::in);
    out.open("fact.out", ios_base::out);
    in >> nrd;
    out << fact(nrd) << endl;
    in.close();
    out.close();
    return 0;
}