def recursive(n, m):
    """ Finds the number of paths between two points with manhattan distance
    n + m. The implementation is recursive and fairly elegant.
    """
    assert n >= 0 and m >= 0
    
    if n == 0 or m == 0:
        return 1
    else:
        return recursive(n - 1, m) + recursive(n, m - 1)