x, y = map(int, input().split())
x2, y2 = map(int, input().split())

d = max(x, y)

on_path = (x2 <= x and y2 <= y) and (max(x2, y2) + max(x - x2, y - y2) == d)

if on_path:
    if x == y and x2 == y2:
        print(d + 1)
    else:
        print(d)
else:
    print(d)