import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt(),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);
        int count = 0;
        for(int i = 1;i<=n;i++){
            if(l[m-1]<=i&&r[0]>=i)count++;
        }
        System.out.println(count);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt(),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);
        int count = 0;
        for(int i = 1;i<=n;i++){
            if(l[m-1]<=i&&r[0]>=i)count++;
        }
        System.out.println(count);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt(),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);
        int count = 0;
        for(int i = 1;i<=n;i++){
            if(l[m-1]<=i&&r[0]>=i)count++;
        }
        System.out.println(count);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt(),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);
        int count = 0;
        for(int i = 1;i<=n;i++){
            if(l[m-1]<=i&&r[0]>=i)count++;
        }
        System.out.println(count);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt() n sc.nextInt() sc.nextInt sc 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 int count = 0; count 0 for(int i = 1;i<=n;i++){
            if(l[m-1]<=i&&r[0]>=i)count++;
        } int i = 1; int i = 1; i 1 i<=n i n i++ i++ i {
            if(l[m-1]<=i&&r[0]>=i)count++;
        } {
            if(l[m-1]<=i&&r[0]>=i)count++;
        } if(l[m-1]<=i&&r[0]>=i)count++; l[m-1]<=i&&r[0]>=i l[m-1]<=i l[m-1] l m-1 m 1 i r[0]>=i r[0] r 0 i count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt(),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);
        int count = 0;
        for(int i = 1;i<=n;i++){
            if(l[m-1]<=i&&r[0]>=i)count++;
        }
        System.out.println(count);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt(),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);
        int count = 0;
        for(int i = 1;i<=n;i++){
            if(l[m-1]<=i&&r[0]>=i)count++;
        }
        System.out.println(count);
    }
} Main
import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt(),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);
        int count = 0;
        for(int i = 1;i<=n;i++){
            if(l[m-1]<=i&&r[0]>=i)count++;
        }
        System.out.println(count);
    }
}
