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

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

int p, n, i, l, r;

int nr0 (int n) {
    int s = 0;
    int exp = 5;
    while (n >= exp) {
        s += (n / exp);
        exp *= 5;
    }
    return s;
}

int cautbin() {
    l = 0;
    r = 1000000000;
    while (l <= r) {
        int m = (l + r) / 2;
        if (nr0(m) < p) l = m + 1;
        else r = m - 1;
    }
    g << l;
}

int main()
{
    f >> p;
    cautbin();

    return 0;
}