#include <fstream>

using namespace std;

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

int p, n, l, r;

int cautbin()
{
    while (l <= r)
    {
        int m;
        int mij = (l + r) / 2;
        n = 0;
        m = mij;
        while (m != 0)
        {
            n += m / 5;
            m /= 5;
        }
        if (n == p)
            return mij - mij % 5;
        else if (n < p)
            l = mij + 1;
        else
            r = mij - 1;
    }
    return -1;
}

int main()
{
    fin >> p;

    l = 0;
    r = 2000000000;

    fout << cautbin();

    fin.close();
    fout.close();
    return 0;
}