import java.util.Scanner;

public class Main {
    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        int A = scanner.nextInt();
        int B = scanner.nextInt();
        int C = scanner.nextInt();
        int D = scanner.nextInt();

        //Not merged case
        if (B <= C || D <= A) {
            System.out.print(0);
            return;
        }

        //One range is in the other range
        if (A <= C && D <= B) {
            System.out.print(D - C);
            return;
        }
        if (C <= A && B <= D) {
            System.out.print(B - A);
        }

        //Merged two range
        if (A < C && B < D) {
            System.out.print(B - C);
            return;
        }

        if (C < A && D < B){
            System.out.print(D - A);
        }
    }
}
/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