#include <iostream>
#include <fstream>

using namespace std;

int nr_div5 (int n)
{
    if (n%5!=0)
        return 0;
    int k=0;
    while (n%5==0)
    {
        n=n/5;
        k++;
    }
    return k;
}
int main()
{
    ifstream fin ("factorial.in");
    ofstream fout ("factorial.out");
    int n, p;
    fin >> p;
    n=0;
    while (p)
    {
        n+=5;
        p=p-nr_div5(n);
    }
    fout << n;
    return 0;
}