#include <fstream>

using namespace std;

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

long long p, n, st, dr, mij, sol = -1, z;

long long zerouri(long long x)
{
    long long s = 0, d = 5;
    while (x / d > 0)
    {
        s = s + x / d;
        d = d * 5;
    }
    return s;
}

int main()
{
    f >> p;
    if (p == 0)
        g << 1;
    else if (p == 1)
        g << 5;
    else
    {
        st = 1;
        dr = 500000000;
        while (st <= dr)
        {
            mij = (st + dr) / 2;
            z = zerouri(mij);
            if (z > p)
                dr = mij - 1;
            else if (z < p)
                st = mij + 1;
            else
            {
                sol = mij;
                dr = mij - 1;
            }
        }
        g << sol;
    }
    f.close();
    g.close();
    return 0;
}