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;
    if (B > C && A < D) {
      ans = Integer.min(B, D) - Integer.max(A, 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;
    if (B > C && A < D) {
      ans = Integer.min(B, D) - Integer.max(A, 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;
    if (B > C && A < D) {
      ans = Integer.min(B, D) - Integer.max(A, 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;
    if (B > C && A < D) {
      ans = Integer.min(B, D) - Integer.max(A, 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 if (B > C && A < D) {
      ans = Integer.min(B, D) - Integer.max(A, C);
    } B > C && A < D B > C B C A < D A D {
      ans = Integer.min(B, D) - Integer.max(A, C);
    } ans = Integer.min(B, D) - Integer.max(A, C) ans Integer.min(B, D) - Integer.max(A, C) Integer.min(B, D) Integer.min Integer B D Integer.max(A, C) Integer.max Integer A 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;
    if (B > C && A < D) {
      ans = Integer.min(B, D) - Integer.max(A, 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;
    if (B > C && A < D) {
      ans = Integer.min(B, D) - Integer.max(A, 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;
    if (B > C && A < D) {
      ans = Integer.min(B, D) - Integer.max(A, C);
    }
    System.out.println(ans);
  }
}