def adjacent_points_max_distance(A):
    n = len(A)
    if(n == 1):
        return -2
    A.sort()
    m = -2
    for i in range(0,n-1):
        m = max(m, abs(A[i] - A[i+1]))
    if(m > 100000000):
        return -1
    return m