import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;

public class Main {
  public static void main(String[] args) throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String[] str = in.readLine().split(" ");
    int a = Integer.parseInt(str[0]);
    int b = Integer.parseInt(str[1]);
    int c = Integer.parseInt(str[2]);
    int d = Integer.parseInt(str[3]);
    System.out.println(Math.min(b,d)-Math.max(a,c)>0?
                       Math.min(b,d)-Math.max(a,c):0);
  }
} import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io import java.io.IOException; IOException java.io public class Main {
  public static void main(String[] args) throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String[] str = in.readLine().split(" ");
    int a = Integer.parseInt(str[0]);
    int b = Integer.parseInt(str[1]);
    int c = Integer.parseInt(str[2]);
    int d = Integer.parseInt(str[3]);
    System.out.println(Math.min(b,d)-Math.max(a,c)>0?
                       Math.min(b,d)-Math.max(a,c):0);
  }
} Main public static void main(String[] args) throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String[] str = in.readLine().split(" ");
    int a = Integer.parseInt(str[0]);
    int b = Integer.parseInt(str[1]);
    int c = Integer.parseInt(str[2]);
    int d = Integer.parseInt(str[3]);
    System.out.println(Math.min(b,d)-Math.max(a,c)>0?
                       Math.min(b,d)-Math.max(a,c):0);
  } main {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String[] str = in.readLine().split(" ");
    int a = Integer.parseInt(str[0]);
    int b = Integer.parseInt(str[1]);
    int c = Integer.parseInt(str[2]);
    int d = Integer.parseInt(str[3]);
    System.out.println(Math.min(b,d)-Math.max(a,c)>0?
                       Math.min(b,d)-Math.max(a,c):0);
  } BufferedReader in = new BufferedReader(new InputStreamReader(System.in)); in new BufferedReader(new InputStreamReader(System.in)) String[] str = in.readLine().split(" "); str in.readLine().split(" ") in.readLine().split in.readLine() in.readLine in " " int a = Integer.parseInt(str[0]); a Integer.parseInt(str[0]) Integer.parseInt Integer str[0] str 0 int b = Integer.parseInt(str[1]); b Integer.parseInt(str[1]) Integer.parseInt Integer str[1] str 1 int c = Integer.parseInt(str[2]); c Integer.parseInt(str[2]) Integer.parseInt Integer str[2] str 2 int d = Integer.parseInt(str[3]); d Integer.parseInt(str[3]) Integer.parseInt Integer str[3] str 3 System.out.println(Math.min(b,d)-Math.max(a,c)>0?
                       Math.min(b,d)-Math.max(a,c):0) System.out.println System.out System System.out Math.min(b,d)-Math.max(a,c)>0?
                       Math.min(b,d)-Math.max(a,c):0 Math.min(b,d)-Math.max(a,c)>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 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 0 String[] args args public class Main {
  public static void main(String[] args) throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String[] str = in.readLine().split(" ");
    int a = Integer.parseInt(str[0]);
    int b = Integer.parseInt(str[1]);
    int c = Integer.parseInt(str[2]);
    int d = Integer.parseInt(str[3]);
    System.out.println(Math.min(b,d)-Math.max(a,c)>0?
                       Math.min(b,d)-Math.max(a,c):0);
  }
} public class Main {
  public static void main(String[] args) throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String[] str = in.readLine().split(" ");
    int a = Integer.parseInt(str[0]);
    int b = Integer.parseInt(str[1]);
    int c = Integer.parseInt(str[2]);
    int d = Integer.parseInt(str[3]);
    System.out.println(Math.min(b,d)-Math.max(a,c)>0?
                       Math.min(b,d)-Math.max(a,c):0);
  }
} Main
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;

public class Main {
  public static void main(String[] args) throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String[] str = in.readLine().split(" ");
    int a = Integer.parseInt(str[0]);
    int b = Integer.parseInt(str[1]);
    int c = Integer.parseInt(str[2]);
    int d = Integer.parseInt(str[3]);
    System.out.println(Math.min(b,d)-Math.max(a,c)>0?
                       Math.min(b,d)-Math.max(a,c):0);
  }
}