#include<iostream>
using namespace std;
int a[10000] = { 0 }, m, l, u, v, sum = 0, z = 0;
int main() {
   
    cin >> l >> m;
    for (int i = 1; i <= m; i++)
    {
        cin >> u >> v;
        for (int i1 = u; i1 <= v; i1++)
        {
            a[i1] = 1;

        }

    }
    for (int i = 0; i <= l; i++)
    {
        if (a[i] ==1) { z++; }

    }
    sum = l + 1 - z;
    cout << sum;


}