import java.util.*;
public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt();
    int B = sc.nextInt();
    int C = sc.nextInt();
    int D = sc.nextInt();
    if(A < C){
      if(B <= C){
        System.out.println(0);
      }else if(D <= B){
        System.out.println(D - C);
      }else{
        System.out.println(B - C);
      }
    }else if(A > C){
      if(D <= A){
        System.out.println(0);
      }else if(B <= D){
        System.out.println(B - A);
      }else{
        System.out.println(D - A);
      }
    }else{
      if(B <= D){
        System.out.println(B - A);
      }else{
        System.out.println(D - C);
      }
    }

  }
}

/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz