#include <fstream>

using namespace std;
int p5 (int n)
{
    int pu5 = 0;
    while (n % 5 == 0)
    {
        pu5++;
        n /= 5;
    }
    return pu5;
}
int main()
{
    ifstream in("fact.in");
    ofstream out("fact.out");
    int p, i, nr5;
    in >> p;
    i = 5;
    nr5 = 0;
    while (nr5 < p)
    {
        nr5 += p5 (i);
        i += 5;
    }
    if (nr5 == p)
        out << i - 5;
    else
        out << -1;
    return 0;
}