import java.util.*;
import static java.lang.Math.*;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		
		// 入力
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		
		// 計算
		int result = 0;
		result = min(min(max(0, d-a), max(0, b-c)), min(max(0, b-a), max(0, d-c)));
		
		// 出力
		System.out.println(result);
	}
}

 import java.util.*; util.* java import static java.lang.Math.*; import static java.lang.Math.*; import static java.lang.Math.*; public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		
		// 入力
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		
		// 計算
		int result = 0;
		result = min(min(max(0, d-a), max(0, b-c)), min(max(0, b-a), max(0, d-c)));
		
		// 出力
		System.out.println(result);
	}
} Main public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		
		// 入力
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		
		// 計算
		int result = 0;
		result = min(min(max(0, d-a), max(0, b-c)), min(max(0, b-a), max(0, d-c)));
		
		// 出力
		System.out.println(result);
	} main {
		Scanner sc = new Scanner(System.in);
		
		// 入力
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		
		// 計算
		int result = 0;
		result = min(min(max(0, d-a), max(0, b-c)), min(max(0, b-a), max(0, d-c)));
		
		// 出力
		System.out.println(result);
	} 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 result = 0; result 0 result = min(min(max(0, d-a), max(0, b-c)), min(max(0, b-a), max(0, d-c))) result min(min(max(0, d-a), max(0, b-c)), min(max(0, b-a), max(0, d-c))) min min(max(0, d-a), max(0, b-c)) min max(0, d-a) max 0 d-a d a max(0, b-c) max 0 b-c b c min(max(0, b-a), max(0, d-c)) min max(0, b-a) max 0 b-a b a max(0, d-c) max 0 d-c d c System.out.println(result) System.out.println System.out System System.out result String[] args args public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		
		// 入力
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		
		// 計算
		int result = 0;
		result = min(min(max(0, d-a), max(0, b-c)), min(max(0, b-a), max(0, d-c)));
		
		// 出力
		System.out.println(result);
	}
} public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		
		// 入力
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		
		// 計算
		int result = 0;
		result = min(min(max(0, d-a), max(0, b-c)), min(max(0, b-a), max(0, d-c)));
		
		// 出力
		System.out.println(result);
	}
} Main
import java.util.*;
import static java.lang.Math.*;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		
		// 入力
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		
		// 計算
		int result = 0;
		result = min(min(max(0, d-a), max(0, b-c)), min(max(0, b-a), max(0, d-c)));
		
		// 出力
		System.out.println(result);
	}
}


