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();
    int ans;
    if(a <= c){
      if(d <= b){
        ans = d - c;
      }else{
        ans = b - c;
      }
    }else{
      if(d <= b){
        ans = d - a;
      }else{
        ans = b - a;
      }
    }
    System.out.println(Math.max(ans, 0));
  }
}

/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