import java.util.*;
public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		int min,max,ans;
		if(b <= c) {
			System.out.println(0);
		}else {
			if(a < c) {
				min = c;
			}else {
				min = a;
			}
			if(b < d) {
				max = b;
			}else {
				max = d;
			}
			if(0 > max - min) {
				ans = 0;
			}else {
				ans = max -min;
			}
			System.out.println(ans);
		}
	}

} import java.util.*; util.* java public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		int min,max,ans;
		if(b <= c) {
			System.out.println(0);
		}else {
			if(a < c) {
				min = c;
			}else {
				min = a;
			}
			if(b < d) {
				max = b;
			}else {
				max = d;
			}
			if(0 > max - min) {
				ans = 0;
			}else {
				ans = max -min;
			}
			System.out.println(ans);
		}
	}

} Main public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		int min,max,ans;
		if(b <= c) {
			System.out.println(0);
		}else {
			if(a < c) {
				min = c;
			}else {
				min = a;
			}
			if(b < d) {
				max = b;
			}else {
				max = d;
			}
			if(0 > max - min) {
				ans = 0;
			}else {
				ans = max -min;
			}
			System.out.println(ans);
		}
	} main {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		int min,max,ans;
		if(b <= c) {
			System.out.println(0);
		}else {
			if(a < c) {
				min = c;
			}else {
				min = a;
			}
			if(b < d) {
				max = b;
			}else {
				max = d;
			}
			if(0 > max - min) {
				ans = 0;
			}else {
				ans = max -min;
			}
			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 min min max max ans; ans if(b <= c) {
			System.out.println(0);
		}else {
			if(a < c) {
				min = c;
			}else {
				min = a;
			}
			if(b < d) {
				max = b;
			}else {
				max = d;
			}
			if(0 > max - min) {
				ans = 0;
			}else {
				ans = max -min;
			}
			System.out.println(ans);
		} b <= c b c {
			System.out.println(0);
		} System.out.println(0) System.out.println System.out System System.out 0 {
			if(a < c) {
				min = c;
			}else {
				min = a;
			}
			if(b < d) {
				max = b;
			}else {
				max = d;
			}
			if(0 > max - min) {
				ans = 0;
			}else {
				ans = max -min;
			}
			System.out.println(ans);
		} 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 if(0 > max - min) {
				ans = 0;
			}else {
				ans = max -min;
			} 0 > max - min 0 max - min max min {
				ans = 0;
			} ans = 0 ans 0 {
				ans = max -min;
			} ans = max -min ans max -min max min 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) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		int min,max,ans;
		if(b <= c) {
			System.out.println(0);
		}else {
			if(a < c) {
				min = c;
			}else {
				min = a;
			}
			if(b < d) {
				max = b;
			}else {
				max = d;
			}
			if(0 > max - min) {
				ans = 0;
			}else {
				ans = max -min;
			}
			System.out.println(ans);
		}
	}

} public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		int min,max,ans;
		if(b <= c) {
			System.out.println(0);
		}else {
			if(a < c) {
				min = c;
			}else {
				min = a;
			}
			if(b < d) {
				max = b;
			}else {
				max = d;
			}
			if(0 > max - min) {
				ans = 0;
			}else {
				ans = max -min;
			}
			System.out.println(ans);
		}
	}

} Main
import java.util.*;
public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		int min,max,ans;
		if(b <= c) {
			System.out.println(0);
		}else {
			if(a < c) {
				min = c;
			}else {
				min = a;
			}
			if(b < d) {
				max = b;
			}else {
				max = d;
			}
			if(0 > max - min) {
				ans = 0;
			}else {
				ans = max -min;
			}
			System.out.println(ans);
		}
	}

}