import java.util.Scanner;

public class Main {

	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		// スペース区切りの整数の入力
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		
		int min = 0;
		int max = 0;
		if ( a < c){
			min = c;
		}else{
			min = a;
		}
		if ( b < d){
			max = b;
		}else{
			max = d;
		}
		int ans = max - min;
		if ( ans > 0){
			System.out.println(ans);
		}else{
			System.out.println(0);
		}
	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		// スペース区切りの整数の入力
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		
		int min = 0;
		int max = 0;
		if ( a < c){
			min = c;
		}else{
			min = a;
		}
		if ( b < d){
			max = b;
		}else{
			max = d;
		}
		int ans = max - min;
		if ( ans > 0){
			System.out.println(ans);
		}else{
			System.out.println(0);
		}
	}
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		// スペース区切りの整数の入力
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		
		int min = 0;
		int max = 0;
		if ( a < c){
			min = c;
		}else{
			min = a;
		}
		if ( b < d){
			max = b;
		}else{
			max = d;
		}
		int ans = max - min;
		if ( ans > 0){
			System.out.println(ans);
		}else{
			System.out.println(0);
		}
	} main {
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		// スペース区切りの整数の入力
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		
		int min = 0;
		int max = 0;
		if ( a < c){
			min = c;
		}else{
			min = a;
		}
		if ( b < d){
			max = b;
		}else{
			max = d;
		}
		int ans = max - min;
		if ( ans > 0){
			System.out.println(ans);
		}else{
			System.out.println(0);
		}
	} 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 min = 0; min 0 int max = 0; max 0 if ( a < c){
			min = c;
		}else{
			min = a;
		} a < c a c {
			min = c;
		} min = c min c {
			min = a;
		} min = a min a if ( b < d){
			max = b;
		}else{
			max = d;
		} b < d b d {
			max = b;
		} max = b max b {
			max = d;
		} max = d max d int ans = max - min; ans max - min max min if ( ans > 0){
			System.out.println(ans);
		}else{
			System.out.println(0);
		} ans > 0 ans 0 {
			System.out.println(ans);
		} System.out.println(ans) System.out.println System.out System System.out ans {
			System.out.println(0);
		} System.out.println(0) System.out.println System.out System System.out 0 String[] args args public class Main {

	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		// スペース区切りの整数の入力
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		
		int min = 0;
		int max = 0;
		if ( a < c){
			min = c;
		}else{
			min = a;
		}
		if ( b < d){
			max = b;
		}else{
			max = d;
		}
		int ans = max - min;
		if ( ans > 0){
			System.out.println(ans);
		}else{
			System.out.println(0);
		}
	}
} public class Main {

	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		// スペース区切りの整数の入力
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		
		int min = 0;
		int max = 0;
		if ( a < c){
			min = c;
		}else{
			min = a;
		}
		if ( b < d){
			max = b;
		}else{
			max = d;
		}
		int ans = max - min;
		if ( ans > 0){
			System.out.println(ans);
		}else{
			System.out.println(0);
		}
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		// スペース区切りの整数の入力
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		
		int min = 0;
		int max = 0;
		if ( a < c){
			min = c;
		}else{
			min = a;
		}
		if ( b < d){
			max = b;
		}else{
			max = d;
		}
		int ans = max - min;
		if ( ans > 0){
			System.out.println(ans);
		}else{
			System.out.println(0);
		}
	}
}
