s = input().split() s = list(map(int, s)) x = s[0] y = s[1] x1 = s[2] y1 = s[3] range_x = x - x1 range_y = y - y1 if range_x < 0: range_x *= -1 if range_y < 0: range_y *= -1 if range_x > range_y: print(range_x) else: print(range_y)