#include <cstdio>
#include <algorithm>

auto nr0(int x) -> int {
    int nr = 0;
    while (x >= 5)
        nr += (x /= 5);
    return nr;
}

auto main() -> int {
    freopen("fact.in", "r", stdin);
    freopen("fact.out", "w", stdout);
    int p;
    scanf("%d", &p);
    int st = 1, dr = 5e8, m, rez;
    while (st < dr) {
        m = (st + dr) / 2;
        if (nr0(m) >= p)
            dr = m;
        else
            st = m + 1;
    }
    rez = st;
    printf("%d\n", rez);
    return 0;
}