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=0;
        int temp;
        if(C <= A){
            temp = A;
            A = C;
            C = temp;
            temp = B;
            B = D;
            D = temp;
        }
        if(B <= C) ans=0;
        else if(D <= B) ans = D - C;
        else ans = B - C;
        System.out.println(ans);

    }
} 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();
        int ans=0;
        int temp;
        if(C <= A){
            temp = A;
            A = C;
            C = temp;
            temp = B;
            B = D;
            D = temp;
        }
        if(B <= C) ans=0;
        else if(D <= B) ans = D - C;
        else ans = B - C;
        System.out.println(ans);

    }
} 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=0;
        int temp;
        if(C <= A){
            temp = A;
            A = C;
            C = temp;
            temp = B;
            B = D;
            D = temp;
        }
        if(B <= C) ans=0;
        else if(D <= B) ans = D - C;
        else ans = B - C;
        System.out.println(ans);

    } main {
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        int C = sc.nextInt();
        int D = sc.nextInt();
        int ans=0;
        int temp;
        if(C <= A){
            temp = A;
            A = C;
            C = temp;
            temp = B;
            B = D;
            D = temp;
        }
        if(B <= C) ans=0;
        else if(D <= B) ans = D - C;
        else ans = B - C;
        System.out.println(ans);

    } 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 int ans=0; ans 0 int temp; temp if(C <= A){
            temp = A;
            A = C;
            C = temp;
            temp = B;
            B = D;
            D = temp;
        } C <= A C A {
            temp = A;
            A = C;
            C = temp;
            temp = B;
            B = D;
            D = temp;
        } temp = A temp A A = C A C C = temp C temp temp = B temp B B = D B D D = temp D temp if(B <= C) ans=0;
        else if(D <= B) ans = D - C;
        else ans = B - C; B <= C B C ans=0 ans 0 if(D <= B) ans = D - C;
        else ans = B - C; D <= B D B ans = D - C ans D - C D C ans = B - C ans B - C B C System.out.println(ans) System.out.println System.out System System.out ans 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();
        int ans=0;
        int temp;
        if(C <= A){
            temp = A;
            A = C;
            C = temp;
            temp = B;
            B = D;
            D = temp;
        }
        if(B <= C) ans=0;
        else if(D <= B) ans = D - C;
        else ans = B - C;
        System.out.println(ans);

    }
} 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=0;
        int temp;
        if(C <= A){
            temp = A;
            A = C;
            C = temp;
            temp = B;
            B = D;
            D = temp;
        }
        if(B <= C) ans=0;
        else if(D <= B) ans = D - C;
        else ans = B - C;
        System.out.println(ans);

    }
} 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();
        int ans=0;
        int temp;
        if(C <= A){
            temp = A;
            A = C;
            C = temp;
            temp = B;
            B = D;
            D = temp;
        }
        if(B <= C) ans=0;
        else if(D <= B) ans = D - C;
        else ans = B - C;
        System.out.println(ans);

    }
}
