import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.PriorityQueue;
import java.util.Scanner;

class Main {
    static final int MOD = 1000000007;
    static final int INF = 1 << 30;

    Main() {
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        int C = sc.nextInt();
        int D = sc.nextInt();
        System.out.println(Math.max(0,Math.min(B,D)-Math.max(A,C)));
    }

    public static void main(String[] args) {
        new Main();
    }
} import java.math.BigInteger; BigInteger java.math import java.util.ArrayList; ArrayList java.util import java.util.Arrays; Arrays java.util import java.util.Collections; Collections java.util import java.util.Comparator; Comparator java.util import java.util.HashMap; HashMap java.util import java.util.HashSet; HashSet java.util import java.util.Iterator; Iterator java.util import java.util.List; List java.util import java.util.Map; Map java.util import java.util.Map.Entry; Entry java.util.Map import java.util.PriorityQueue; PriorityQueue java.util import java.util.Scanner; Scanner java.util class Main {
    static final int MOD = 1000000007;
    static final int INF = 1 << 30;

    Main() {
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        int C = sc.nextInt();
        int D = sc.nextInt();
        System.out.println(Math.max(0,Math.min(B,D)-Math.max(A,C)));
    }

    public static void main(String[] args) {
        new Main();
    }
} Main static final int MOD = 1000000007; MOD 1000000007 static final int INF = 1 << 30; INF 1 << 30 1 30 Main() {
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        int C = sc.nextInt();
        int D = sc.nextInt();
        System.out.println(Math.max(0,Math.min(B,D)-Math.max(A,C)));
    } Main {
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        int C = sc.nextInt();
        int D = sc.nextInt();
        System.out.println(Math.max(0,Math.min(B,D)-Math.max(A,C)));
    } 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 System.out.println(Math.max(0,Math.min(B,D)-Math.max(A,C))) System.out.println System.out System System.out Math.max(0,Math.min(B,D)-Math.max(A,C)) Math.max Math 0 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 public static void main(String[] args) {
        new Main();
    } main {
        new Main();
    } new Main() String[] args args
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.PriorityQueue;
import java.util.Scanner;

class Main {
    static final int MOD = 1000000007;
    static final int INF = 1 << 30;

    Main() {
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        int C = sc.nextInt();
        int D = sc.nextInt();
        System.out.println(Math.max(0,Math.min(B,D)-Math.max(A,C)));
    }

    public static void main(String[] args) {
        new Main();
    }
}
