import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		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 (r[0] - l[m-1] < 0) {
			System.out.println(0);
			return;
		}
		System.out.println(r[0] - l[m-1] + 1);
	}
} import java.util.*; util.* java public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		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 (r[0] - l[m-1] < 0) {
			System.out.println(0);
			return;
		}
		System.out.println(r[0] - l[m-1] + 1);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		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 (r[0] - l[m-1] < 0) {
			System.out.println(0);
			return;
		}
		System.out.println(r[0] - l[m-1] + 1);
	} main {
		Scanner sc = new Scanner(System.in);
		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 (r[0] - l[m-1] < 0) {
			System.out.println(0);
			return;
		}
		System.out.println(r[0] - l[m-1] + 1);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) 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 (r[0] - l[m-1] < 0) {
			System.out.println(0);
			return;
		} r[0] - l[m-1] < 0 r[0] - l[m-1] r[0] r 0 l[m-1] l m-1 m 1 0 {
			System.out.println(0);
			return;
		} System.out.println(0) System.out.println System.out System System.out 0 return; 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 String[] args args public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		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 (r[0] - l[m-1] < 0) {
			System.out.println(0);
			return;
		}
		System.out.println(r[0] - l[m-1] + 1);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		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 (r[0] - l[m-1] < 0) {
			System.out.println(0);
			return;
		}
		System.out.println(r[0] - l[m-1] + 1);
	}
} Main
import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		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 (r[0] - l[m-1] < 0) {
			System.out.println(0);
			return;
		}
		System.out.println(r[0] - l[m-1] + 1);
	}
}