#include <fstream>
using namespace std;
ifstream in ("fact.in");
ofstream out ("fact.out");
const int N = 400000055;
int p;

int nrZerouri(int x)
{
    int p5 = 5, nrZ = 0;
    while (x/p5)
    {
        nrZ += x/p5;
        p5 *= 5;
    }
    return nrZ;
}

int cautareBinara(int st, int dr)
{
    int m = (st+dr)/2, nrZ = nrZerouri(m);
    while (st <= dr)
    {
        if (nrZ == p) break;
        else if (nrZ < p) st = m+1;
             else dr = m-1;
        m = (st+dr)/2; nrZ = nrZerouri(m);
    }
    if (st > dr) return -1;
    else
    {
        m = (st+dr)/2;
        while (nrZerouri(m) == nrZerouri(m-1)) m--;
        return m;
    }
}

int main()
{
    in >> p;
    if (p == 0) out << "1\n";
    else out << cautareBinara(1, N) << '\n';
    out.close(); return 0;
}