x,y,w,h = map(int,input().split())

if h > 1000 or x < 0 or y < 0 or w < 0:
    print('wrong input')
else: 
    x_length = w-x
    y_length = h-y
    if x_length < y_length:
        print(x_length)
    else:
        print(y_length)