a = input().split() b = int(a[0]) c = int(a[1]) d = int(a[2]) e = int(a[3]) if b-d<0: x = (b-d)*-1 else: x = b-d if c-e<0: y = (c-e)*-1 else: x = c-e if x > y: print(x) else: print(y)