def fibIter(n):
    if n == 0 or n == 1:
        return 0
    elif n == 2:
        return 1
    else:
        ciag = [0, 0, 1]
        for i in range(3, n + 1):
            ciag.insert(i, ciag[i - 3] + ciag[i - 2] + ciag[i - 1])
        return ciag[n]