#include <fstream>

using namespace std;

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

long long fact_zero(int n) {
    long long s = 0;
    while (n >= 5) {
        s += n / 5;
        n /= 5;
    }
    return s;
}

int cautbin(long long x) {
    int r = 0, pas = 1 << 28;
    while (pas != 0) {
        if (fact_zero(r + pas) < x) {
            r += pas;
        }
        pas >>= 1;
    }
    r++;
    if (fact_zero(r) == x) return r;
    return -1;
}

int main()
{
    long long p;
    in >> p;
    out << cautbin(p);
}