import java.io.IOException;
import java.io.InputStream;
import java.util.NoSuchElementException;

public class Main {
	public static void main(String[] args){
		FastScanner sc = new FastScanner();
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		if(b <= c || a >= d){
			System.out.println(0);
		}else{
			System.out.println(Math.min(b, d) -  Math.max(a, c));
		}

	}
}

class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;
    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }
    private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
    private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
    public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte();}
    public long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }
    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
        return (int) nl;
    }
} import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.util.NoSuchElementException; NoSuchElementException java.util public class Main {
	public static void main(String[] args){
		FastScanner sc = new FastScanner();
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		if(b <= c || a >= d){
			System.out.println(0);
		}else{
			System.out.println(Math.min(b, d) -  Math.max(a, c));
		}

	}
} Main public static void main(String[] args){
		FastScanner sc = new FastScanner();
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		if(b <= c || a >= d){
			System.out.println(0);
		}else{
			System.out.println(Math.min(b, d) -  Math.max(a, c));
		}

	} main {
		FastScanner sc = new FastScanner();
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		if(b <= c || a >= d){
			System.out.println(0);
		}else{
			System.out.println(Math.min(b, d) -  Math.max(a, c));
		}

	} FastScanner sc = new FastScanner(); sc new FastScanner() 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 if(b <= c || a >= d){
			System.out.println(0);
		}else{
			System.out.println(Math.min(b, d) -  Math.max(a, c));
		} b <= c || a >= d b <= c b c a >= d a d {
			System.out.println(0);
		} System.out.println(0) System.out.println System.out System System.out 0 {
			System.out.println(Math.min(b, d) -  Math.max(a, c));
		} System.out.println(Math.min(b, d) -  Math.max(a, c)) System.out.println System.out System System.out 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 String[] args args class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;
    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }
    private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
    private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
    public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte();}
    public long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }
    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
        return (int) nl;
    }
} FastScanner private final InputStream in = System.in; in System.in System System.in private final byte[] buffer = new byte[1024]; buffer new byte[1024] 1024 private int ptr = 0; ptr 0 private int buflen = 0; buflen 0 private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    } hasNextByte {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    } if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        } ptr < buflen ptr buflen {
            return true;
        } return true; true {
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        } ptr = 0 ptr 0 try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } IOException e {
                e.printStackTrace();
            } e.printStackTrace() e.printStackTrace e {
                buflen = in.read(buffer);
            } buflen = in.read(buffer) buflen in.read(buffer) in.read in buffer if (buflen <= 0) {
                return false;
            } buflen <= 0 buflen 0 {
                return false;
            } return false; false return true; true private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;} readByte { if (hasNextByte()) return buffer[ptr++]; else return -1;} if (hasNextByte()) return buffer[ptr++]; else return -1; hasNextByte() hasNextByte return buffer[ptr++]; buffer[ptr++] buffer ptr++ ptr return -1; -1 1 private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;} isPrintableChar { return 33 <= c && c <= 126;} return 33 <= c && c <= 126; 33 <= c && c <= 126 33 <= c 33 c c <= 126 c 126 int c c public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte();} hasNext { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte();} while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; hasNextByte() && !isPrintableChar(buffer[ptr]) hasNextByte() hasNextByte !isPrintableChar(buffer[ptr]) isPrintableChar(buffer[ptr]) isPrintableChar buffer[ptr] buffer ptr ptr++ ptr return hasNextByte(); hasNextByte() hasNextByte public long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    } nextLong {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    } if (!hasNext()) throw new NoSuchElementException(); !hasNext() hasNext() hasNext throw new NoSuchElementException(); new NoSuchElementException() long n = 0; n 0 boolean minus = false; minus false int b = readByte(); b readByte() readByte if (b == '-') {
            minus = true;
            b = readByte();
        } b == '-' b '-' {
            minus = true;
            b = readByte();
        } minus = true minus true b = readByte() b readByte() readByte if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        } b < '0' || '9' < b b < '0' b '0' '9' < b '9' b {
            throw new NumberFormatException();
        } throw new NumberFormatException(); new NumberFormatException() while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        } true {
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        } if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            } '0' <= b && b <= '9' '0' <= b '0' b b <= '9' b '9' {
                n *= 10;
                n += b - '0';
            } n *= 10 n 10 n += b - '0' n b - '0' b '0' if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            } b == -1 || !isPrintableChar(b) b == -1 b -1 1 !isPrintableChar(b) isPrintableChar(b) isPrintableChar b {
                return minus ? -n : n;
            } return minus ? -n : n; minus ? -n : n minus -n n n {
                throw new NumberFormatException();
            } throw new NumberFormatException(); new NumberFormatException() b = readByte() b readByte() readByte public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
        return (int) nl;
    } nextInt {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
        return (int) nl;
    } long nl = nextLong(); nl nextLong() nextLong if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException(); nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE nl < Integer.MIN_VALUE nl Integer.MIN_VALUE Integer Integer.MIN_VALUE nl > Integer.MAX_VALUE nl Integer.MAX_VALUE Integer Integer.MAX_VALUE throw new NumberFormatException(); new NumberFormatException() return (int) nl; (int) nl public class Main {
	public static void main(String[] args){
		FastScanner sc = new FastScanner();
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		if(b <= c || a >= d){
			System.out.println(0);
		}else{
			System.out.println(Math.min(b, d) -  Math.max(a, c));
		}

	}
} public class Main {
	public static void main(String[] args){
		FastScanner sc = new FastScanner();
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		if(b <= c || a >= d){
			System.out.println(0);
		}else{
			System.out.println(Math.min(b, d) -  Math.max(a, c));
		}

	}
} Main
import java.io.IOException;
import java.io.InputStream;
import java.util.NoSuchElementException;

public class Main {
	public static void main(String[] args){
		FastScanner sc = new FastScanner();
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		if(b <= c || a >= d){
			System.out.println(0);
		}else{
			System.out.println(Math.min(b, d) -  Math.max(a, c));
		}

	}
}

class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;
    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }
    private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
    private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
    public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte();}
    public long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }
    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
        return (int) nl;
    }
}