#include <fstream>
using namespace std;

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

int nrzero(int k)
{
    int f = 5, s = 0;
    while (f<=k)
    {
        s = s + k/f;
        f = f*5;
    }
    return s;
}

int main()
{
    int st = 1, dr = 2000000000, p, mij;
    fin >> p;
    while (st <= dr)
    {
        mij = (st+dr)/2;
        if (p <= nrzero(mij))
            dr = mij - 1;
        else
            st = mij + 1;
    }
    if (nrzero(st) != p)
        fout << -1;
    else
        fout << st;
    return 0;
}