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[] imos = new int[n + 1];
        for (int i = 0; i < m; i++) {
            imos[sc.nextInt() - 1]++;
            imos[sc.nextInt()]--;
        }
        int count = 0;
        for (int i = 1; i <= n; i++) {
            if (imos[i - 1] == m) {
                count++;
            }
            imos[i] += imos[i - 1];
        }
		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();
		int m = sc.nextInt();
		int[] imos = new int[n + 1];
        for (int i = 0; i < m; i++) {
            imos[sc.nextInt() - 1]++;
            imos[sc.nextInt()]--;
        }
        int count = 0;
        for (int i = 1; i <= n; i++) {
            if (imos[i - 1] == m) {
                count++;
            }
            imos[i] += imos[i - 1];
        }
		System.out.println(count);
   }
} Main public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		int[] imos = new int[n + 1];
        for (int i = 0; i < m; i++) {
            imos[sc.nextInt() - 1]++;
            imos[sc.nextInt()]--;
        }
        int count = 0;
        for (int i = 1; i <= n; i++) {
            if (imos[i - 1] == m) {
                count++;
            }
            imos[i] += imos[i - 1];
        }
		System.out.println(count);
   } main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		int[] imos = new int[n + 1];
        for (int i = 0; i < m; i++) {
            imos[sc.nextInt() - 1]++;
            imos[sc.nextInt()]--;
        }
        int count = 0;
        for (int i = 1; i <= n; i++) {
            if (imos[i - 1] == m) {
                count++;
            }
            imos[i] += imos[i - 1];
        }
		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 int m = sc.nextInt(); m sc.nextInt() sc.nextInt sc int[] imos = new int[n + 1]; imos new int[n + 1] n + 1 n 1 for (int i = 0; i < m; i++) {
            imos[sc.nextInt() - 1]++;
            imos[sc.nextInt()]--;
        } int i = 0; int i = 0; i 0 i < m i m i++ i++ i {
            imos[sc.nextInt() - 1]++;
            imos[sc.nextInt()]--;
        } {
            imos[sc.nextInt() - 1]++;
            imos[sc.nextInt()]--;
        } imos[sc.nextInt() - 1]++ imos[sc.nextInt() - 1] imos sc.nextInt() - 1 sc.nextInt() sc.nextInt sc 1 imos[sc.nextInt()]-- imos[sc.nextInt()] imos sc.nextInt() sc.nextInt sc int count = 0; count 0 for (int i = 1; i <= n; i++) {
            if (imos[i - 1] == m) {
                count++;
            }
            imos[i] += imos[i - 1];
        } int i = 1; int i = 1; i 1 i <= n i n i++ i++ i {
            if (imos[i - 1] == m) {
                count++;
            }
            imos[i] += imos[i - 1];
        } {
            if (imos[i - 1] == m) {
                count++;
            }
            imos[i] += imos[i - 1];
        } if (imos[i - 1] == m) {
                count++;
            } imos[i - 1] == m imos[i - 1] imos i - 1 i 1 m {
                count++;
            } count++ count imos[i] += imos[i - 1] imos[i] imos i imos[i - 1] imos i - 1 i 1 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();
		int m = sc.nextInt();
		int[] imos = new int[n + 1];
        for (int i = 0; i < m; i++) {
            imos[sc.nextInt() - 1]++;
            imos[sc.nextInt()]--;
        }
        int count = 0;
        for (int i = 1; i <= n; i++) {
            if (imos[i - 1] == m) {
                count++;
            }
            imos[i] += imos[i - 1];
        }
		System.out.println(count);
   }
} public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		int[] imos = new int[n + 1];
        for (int i = 0; i < m; i++) {
            imos[sc.nextInt() - 1]++;
            imos[sc.nextInt()]--;
        }
        int count = 0;
        for (int i = 1; i <= n; i++) {
            if (imos[i - 1] == m) {
                count++;
            }
            imos[i] += imos[i - 1];
        }
		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();
		int m = sc.nextInt();
		int[] imos = new int[n + 1];
        for (int i = 0; i < m; i++) {
            imos[sc.nextInt() - 1]++;
            imos[sc.nextInt()]--;
        }
        int count = 0;
        for (int i = 1; i <= n; i++) {
            if (imos[i - 1] == m) {
                count++;
            }
            imos[i] += imos[i - 1];
        }
		System.out.println(count);
   }
}
