gx, gy = gets.split.map(&:to_i)
px, py = gets.split.map(&:to_i)

if [gx.abs == gy.abs,
    px.abs == py.abs, 
    (px > 0) == (gx > 0),
    (py > 0) == (gy > 0),
    px < gx ].all?
    
    puts [gx.abs,gy.abs].max + 1
else
    puts [gx.abs,gy.abs].max
end