#include <fstream>

using namespace std;

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

int nrOf0(int n)
{
    int i, c = 0;
    for(i = 5; n/i >= 1; i *= 5)
        c += n/i;
    return c;
}

int p, st = 1, dr = 50000000, mid;

int main()
{
    f >> p;
    while(st <= dr)
    {
        mid = (st + dr)/2;
        if(nrOf0(mid) < p)
            st = mid + 1;
        else
            dr = mid - 1;
    }

    if(nrOf0(st) == p)
        g << st;
    else
        g << -1;

}