#include<stdio.h>
int main() {
    int l, s, n, i, j, a;
    int arr1[100] = { 0 };
    int arr2[100] = { 0 };
    int arr[10000] = { 0 };
    i = j = 0;
    scanf("%d %d", &l, &n);
   // a = l-1;
   // int arr[a] = {0};
    for (i = 0; i < n; i++) {
        scanf("%d %d", &arr1[i], &arr2[i]);
    }
    for (i = arr1[0]; i <= arr2[0]; i++) {
        arr[i - 1] = 1;
    }
    if (arr1[1]!=0)
    {
        for (i = arr1[1]; i <= arr2[1]; i++) {
            arr[i - 1] = 1;
        }
    }
    if (arr1[2]!=0)
    {
        for (i = arr1[2]; i <= arr2[2]; i++) {
            arr[i - 1] = 1;
        }
    }
    for (i = 0; i <= 10000; i++) {
        if (arr[i]==1)
        {
            j++;
        }
    }
    a = l - j + 1;
    printf("%d", a);
    return 0;
}