import java.util.Arrays;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		@SuppressWarnings("unused")
		int n = sc.nextInt();
		int m = sc.nextInt();
		int[] l = new int[m];
		int[] r = new int[m];

		for (int i = 0; i < m; i++) {
			l[i] = sc.nextInt();
			r[i] = sc.nextInt();
		}

		Arrays.sort(l);
		Arrays.sort(r);

		if (l[m - 1] > r[0]) {
			System.out.println(0);
		} else {
			System.out.println(r[0] - l[m - 1] + 1);
		}
		sc.close();
	}
} import java.util.Arrays; Arrays java.util import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		@SuppressWarnings("unused")
		int n = sc.nextInt();
		int m = sc.nextInt();
		int[] l = new int[m];
		int[] r = new int[m];

		for (int i = 0; i < m; i++) {
			l[i] = sc.nextInt();
			r[i] = sc.nextInt();
		}

		Arrays.sort(l);
		Arrays.sort(r);

		if (l[m - 1] > r[0]) {
			System.out.println(0);
		} else {
			System.out.println(r[0] - l[m - 1] + 1);
		}
		sc.close();
	}
} Main public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		@SuppressWarnings("unused")
		int n = sc.nextInt();
		int m = sc.nextInt();
		int[] l = new int[m];
		int[] r = new int[m];

		for (int i = 0; i < m; i++) {
			l[i] = sc.nextInt();
			r[i] = sc.nextInt();
		}

		Arrays.sort(l);
		Arrays.sort(r);

		if (l[m - 1] > r[0]) {
			System.out.println(0);
		} else {
			System.out.println(r[0] - l[m - 1] + 1);
		}
		sc.close();
	} main {

		Scanner sc = new Scanner(System.in);

		@SuppressWarnings("unused")
		int n = sc.nextInt();
		int m = sc.nextInt();
		int[] l = new int[m];
		int[] r = new int[m];

		for (int i = 0; i < m; i++) {
			l[i] = sc.nextInt();
			r[i] = sc.nextInt();
		}

		Arrays.sort(l);
		Arrays.sort(r);

		if (l[m - 1] > r[0]) {
			System.out.println(0);
		} else {
			System.out.println(r[0] - l[m - 1] + 1);
		}
		sc.close();
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) @SuppressWarnings("unused")
		int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int m = sc.nextInt(); m sc.nextInt() sc.nextInt sc int[] l = new int[m]; l new int[m] m int[] r = new int[m]; r new int[m] m for (int i = 0; i < m; i++) {
			l[i] = sc.nextInt();
			r[i] = sc.nextInt();
		} int i = 0; int i = 0; i 0 i < m i m i++ i++ i {
			l[i] = sc.nextInt();
			r[i] = sc.nextInt();
		} {
			l[i] = sc.nextInt();
			r[i] = sc.nextInt();
		} l[i] = sc.nextInt() l[i] l i sc.nextInt() sc.nextInt sc r[i] = sc.nextInt() r[i] r i sc.nextInt() sc.nextInt sc Arrays.sort(l) Arrays.sort Arrays l Arrays.sort(r) Arrays.sort Arrays r if (l[m - 1] > r[0]) {
			System.out.println(0);
		} else {
			System.out.println(r[0] - l[m - 1] + 1);
		} l[m - 1] > r[0] l[m - 1] l m - 1 m 1 r[0] r 0 {
			System.out.println(0);
		} System.out.println(0) System.out.println System.out System System.out 0 {
			System.out.println(r[0] - l[m - 1] + 1);
		} System.out.println(r[0] - l[m - 1] + 1) System.out.println System.out System System.out r[0] - l[m - 1] + 1 r[0] - l[m - 1] r[0] r 0 l[m - 1] l m - 1 m 1 1 sc.close() sc.close sc String[] args args public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		@SuppressWarnings("unused")
		int n = sc.nextInt();
		int m = sc.nextInt();
		int[] l = new int[m];
		int[] r = new int[m];

		for (int i = 0; i < m; i++) {
			l[i] = sc.nextInt();
			r[i] = sc.nextInt();
		}

		Arrays.sort(l);
		Arrays.sort(r);

		if (l[m - 1] > r[0]) {
			System.out.println(0);
		} else {
			System.out.println(r[0] - l[m - 1] + 1);
		}
		sc.close();
	}
} public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		@SuppressWarnings("unused")
		int n = sc.nextInt();
		int m = sc.nextInt();
		int[] l = new int[m];
		int[] r = new int[m];

		for (int i = 0; i < m; i++) {
			l[i] = sc.nextInt();
			r[i] = sc.nextInt();
		}

		Arrays.sort(l);
		Arrays.sort(r);

		if (l[m - 1] > r[0]) {
			System.out.println(0);
		} else {
			System.out.println(r[0] - l[m - 1] + 1);
		}
		sc.close();
	}
} Main
import java.util.Arrays;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		@SuppressWarnings("unused")
		int n = sc.nextInt();
		int m = sc.nextInt();
		int[] l = new int[m];
		int[] r = new int[m];

		for (int i = 0; i < m; i++) {
			l[i] = sc.nextInt();
			r[i] = sc.nextInt();
		}

		Arrays.sort(l);
		Arrays.sort(r);

		if (l[m - 1] > r[0]) {
			System.out.println(0);
		} else {
			System.out.println(r[0] - l[m - 1] + 1);
		}
		sc.close();
	}
}