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

if gx.abs == gy.abs && px / gx == py / gy && px / gx < 1
    puts [gx.abs,gy.abs].max + 1
else
    puts [gx.abs,gy.abs].max
end