import java.util.Scanner;

class Main{
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        int a = in.nextInt(), b = in.nextInt(),
            c = in.nextInt(), d = in.nextInt();
        
        if((c > b && d > b) || (a > d && b > d)){
            System.out.println(0);
            return;
        }
        int ans = 0;
        if(a > c){
            ans = d - a - Math.max(0, d - b);
        }else{
            ans = b - c - Math.max(0, b - d);
        }
        System.out.println(ans);
    }
}
/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