#include <bits/stdc++.h>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
unsigned long long n, rez;
unsigned long long calc(unsigned long long);
int main()
{
    f >> n;
    if (!n)
        g << 1, g.flush(), exit(0);
    unsigned long long st = 1ll, dr = n * 5;
    while (st <= dr)
    {
        unsigned long long mid = st + ((dr - st) >> 1);
        unsigned long long ax = calc(mid);
        if (n == ax)
            g << mid - mid % 5, g.flush(), exit(0);
        if (ax < n)
            st = mid + 1;
        else
            dr = mid - 1;
    }
    g << -1;
    return 0;
}
unsigned long long calc(unsigned long long x)
{
    unsigned long long p = 5, r = 0;
    while (p <= x)
        r += x / p, p *= 5;
    return r;
}