import java.util.Scanner
import java.lang.Math.abs

object Problem208 {

  def proc(target: (Int, Int), hohei: (Int, Int)): Int = {
    val t = (abs(target._1), abs(target._2))
    val h = (abs(hohei._1), abs(hohei._2))

    // 直線上に歩兵がいる場合だけ1歩余計に掛かる
    if (t._1 == t._2 && h._1 == h._2 && t._1 > h._1) {
      t._1 + 1
    } else {
      if (t._1 > t._2) t._1 else t._2
    }
  }

  def main(args: Array[String]) {
    val sc = new Scanner(System.in)
    val target = (sc.nextInt, sc.nextInt)
    val hohei = (sc.nextInt, sc.nextInt)

    val result = proc(target, hohei)
    println(result)
  }
}