import java.util.Scanner;

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 count=0;
        for (int i = A; i < B; i++) {
            if (C <= i && i < D) {
                count++;
            }
        }
        System.out.println(count);
    }
} import java.util.Scanner; Scanner 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 count=0;
        for (int i = A; i < B; i++) {
            if (C <= i && i < D) {
                count++;
            }
        }
        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 count=0;
        for (int i = A; i < B; i++) {
            if (C <= i && i < D) {
                count++;
            }
        }
        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 count=0;
        for (int i = A; i < B; i++) {
            if (C <= i && i < D) {
                count++;
            }
        }
        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 count=0; count 0 for (int i = A; i < B; i++) {
            if (C <= i && i < D) {
                count++;
            }
        } int i = A; int i = A; i A i < B i B i++ i++ i {
            if (C <= i && i < D) {
                count++;
            }
        } {
            if (C <= i && i < D) {
                count++;
            }
        } if (C <= i && i < D) {
                count++;
            } C <= i && i < D C <= i C i i < D i D {
                count++;
            } count++ count 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 count=0;
        for (int i = A; i < B; i++) {
            if (C <= i && i < D) {
                count++;
            }
        }
        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 count=0;
        for (int i = A; i < B; i++) {
            if (C <= i && i < D) {
                count++;
            }
        }
        System.out.println(count);
    }
} Main
import java.util.Scanner;

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 count=0;
        for (int i = A; i < B; i++) {
            if (C <= i && i < D) {
                count++;
            }
        }
        System.out.println(count);
    }
}