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

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

if abs(x) == abs(y) and abs(x2) == abs(y2) and x * x2 > 0 and y * y2 > 0 and abs(x) > abs(x2):
    
    print(abs(x) + 1)
else:
    
    print(max(abs(x), abs(y)))