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();

        sc.close();

        int diff = Math.min(B, D) - Math.max(A, C);
        int count = diff < 0 ? 0 : diff;

        System.out.println(count);

    }
} import java.util.*; util.* java 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();

        sc.close();

        int diff = Math.min(B, D) - Math.max(A, C);
        int count = diff < 0 ? 0 : diff;

        System.out.println(count);

    }
} 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();

        sc.close();

        int diff = Math.min(B, D) - Math.max(A, C);
        int count = diff < 0 ? 0 : diff;

        System.out.println(count);

    } main {
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        int C = sc.nextInt();
        int D = sc.nextInt();

        sc.close();

        int diff = Math.min(B, D) - Math.max(A, C);
        int count = diff < 0 ? 0 : diff;

        System.out.println(count);

    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int A = sc.nextInt(); A sc.nextInt() sc.nextInt sc int B = sc.nextInt(); B sc.nextInt() sc.nextInt sc int C = sc.nextInt(); C sc.nextInt() sc.nextInt sc int D = sc.nextInt(); D sc.nextInt() sc.nextInt sc sc.close() sc.close sc int diff = Math.min(B, D) - Math.max(A, C); diff Math.min(B, D) - Math.max(A, C) Math.min(B, D) Math.min Math B D Math.max(A, C) Math.max Math A C int count = diff < 0 ? 0 : diff; count diff < 0 ? 0 : diff diff < 0 diff 0 0 diff System.out.println(count) System.out.println System.out System System.out count String[] args args 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();

        sc.close();

        int diff = Math.min(B, D) - Math.max(A, C);
        int count = diff < 0 ? 0 : diff;

        System.out.println(count);

    }
} 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();

        sc.close();

        int diff = Math.min(B, D) - Math.max(A, C);
        int count = diff < 0 ? 0 : diff;

        System.out.println(count);

    }
} Main
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();

        sc.close();

        int diff = Math.min(B, D) - Math.max(A, C);
        int count = diff < 0 ? 0 : diff;

        System.out.println(count);

    }
}