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

long long f(long long nr);

int main() {
    ifstream in("fact.in");
    long long n, p = 0, q = (1ll << 60);

    in >> n;

    while (q > 0) {
        if ( f(p + q) < n )
            p += q;
        q /= 2;
    }
    p++;
    if ( f(p) != n ) {
        ofstream out("fact.out");
        out << -1 << ' ' << p;
        return 0;
    }
    ofstream out("fact.out");
    out << p;

    return 0;
}


long long f(long long nr) {
    long long r = 0;
    nr /= 5;
    while (nr > 0) {
        r += nr;
        nr /= 5;
    }
    return r;
}