static ulong fibonacciIteratiu(ulong n)
{
    ulong n1, n2, i, aux;
    if (n == 0 || n == 1) return n;
    else
    {
        n1 = 0;
        n2 = 1;
        i = 1;
        while (i < n)
        {
            aux = n2;
            n2 = n2 + n1;
            n1 = aux;
            i++;
        }
        return n2;
    }
}