

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int M = sc.nextInt();

        int left = 1;
        int right = N;
        for(int i = 0; i < M; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            left = Math.max(left,a);
            right = Math.min(right,b);
        }
        System.out.println(Math.max(right-left+1, 0));
    }
} import java.util.Scanner; Scanner 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 left = 1;
        int right = N;
        for(int i = 0; i < M; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            left = Math.max(left,a);
            right = Math.min(right,b);
        }
        System.out.println(Math.max(right-left+1, 0));
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int M = sc.nextInt();

        int left = 1;
        int right = N;
        for(int i = 0; i < M; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            left = Math.max(left,a);
            right = Math.min(right,b);
        }
        System.out.println(Math.max(right-left+1, 0));
    } main {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int M = sc.nextInt();

        int left = 1;
        int right = N;
        for(int i = 0; i < M; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            left = Math.max(left,a);
            right = Math.min(right,b);
        }
        System.out.println(Math.max(right-left+1, 0));
    } 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 left = 1; left 1 int right = N; right N for(int i = 0; i < M; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            left = Math.max(left,a);
            right = Math.min(right,b);
        } int i = 0; int i = 0; i 0 i < M i M i++ i++ i {
            int a = sc.nextInt();
            int b = sc.nextInt();
            left = Math.max(left,a);
            right = Math.min(right,b);
        } {
            int a = sc.nextInt();
            int b = sc.nextInt();
            left = Math.max(left,a);
            right = Math.min(right,b);
        } int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc int b = sc.nextInt(); b sc.nextInt() sc.nextInt sc left = Math.max(left,a) left Math.max(left,a) Math.max Math left a right = Math.min(right,b) right Math.min(right,b) Math.min Math right b System.out.println(Math.max(right-left+1, 0)) System.out.println System.out System System.out Math.max(right-left+1, 0) Math.max Math right-left+1 right-left right left 1 0 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 left = 1;
        int right = N;
        for(int i = 0; i < M; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            left = Math.max(left,a);
            right = Math.min(right,b);
        }
        System.out.println(Math.max(right-left+1, 0));
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int M = sc.nextInt();

        int left = 1;
        int right = N;
        for(int i = 0; i < M; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            left = Math.max(left,a);
            right = Math.min(right,b);
        }
        System.out.println(Math.max(right-left+1, 0));
    }
} Main


import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int M = sc.nextInt();

        int left = 1;
        int right = N;
        for(int i = 0; i < M; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            left = Math.max(left,a);
            right = Math.min(right,b);
        }
        System.out.println(Math.max(right-left+1, 0));
    }
}
