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;
		for (int i = 0; i <= 100; i++) {
			if (A < i && B >= i && C < i && D >= i) {
				ans++;
			}
		}
		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;
		for (int i = 0; i <= 100; i++) {
			if (A < i && B >= i && C < i && D >= i) {
				ans++;
			}
		}
		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;
		for (int i = 0; i <= 100; i++) {
			if (A < i && B >= i && C < i && D >= i) {
				ans++;
			}
		}
		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;
		for (int i = 0; i <= 100; i++) {
			if (A < i && B >= i && C < i && D >= i) {
				ans++;
			}
		}
		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 for (int i = 0; i <= 100; i++) {
			if (A < i && B >= i && C < i && D >= i) {
				ans++;
			}
		} int i = 0; int i = 0; i 0 i <= 100 i 100 i++ i++ i {
			if (A < i && B >= i && C < i && D >= i) {
				ans++;
			}
		} {
			if (A < i && B >= i && C < i && D >= i) {
				ans++;
			}
		} if (A < i && B >= i && C < i && D >= i) {
				ans++;
			} A < i && B >= i && C < i && D >= i C < i A < i && B >= i && C < i && D >= i A < i A i B >= i B i C < i C i D >= i D i {
				ans++;
			} ans++ ans 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;
		for (int i = 0; i <= 100; i++) {
			if (A < i && B >= i && C < i && D >= i) {
				ans++;
			}
		}
		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;
		for (int i = 0; i <= 100; i++) {
			if (A < i && B >= i && C < i && D >= i) {
				ans++;
			}
		}
		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;
		for (int i = 0; i <= 100; i++) {
			if (A < i && B >= i && C < i && D >= i) {
				ans++;
			}
		}
		System.out.println(ans);
	}
}
