#include <stdio.h>
int main(){
    int l, m;
    int area[100][2];
    scanf("%d %d", &l, &m);
    int num = 0;
    for (int i = 0; i < m; i++)
    {
        scanf(" %d %d", &area[i][0], &area[i][1]);
    }
    for (int j = 0; j < l; j++)
    {
        int flag = 0;
        for (int k = 0; k < m; k++)
        {
            if ((j>=area[k][0])&&(j<=area[k][1]))
            {
                flag = 1;
            }
            
        }
        if (flag==1)
        {
            num = num + 1;
        }
    }
    printf("%d", l + 1 - num);
    return 0;
}