#include <bits/stdc++.h>
using namespace std;

const int N = 110;
struct Node {
    int st;
    int ed;
} seg[N];

bool cmp(Node a, Node b) {
    if (a.st == b.st) return a.ed < b.ed;
    return a.st < b.st;
}

int m, L;

int main() {
    cin >> L >> m;

    for (int i = 0; i < m; i++) cin >> seg[i].st >> seg[i].ed;
    sort(seg, seg + m, cmp);

    int res = L + 1;

    int st = seg[0].st, ed = seg[0].ed;
    for (int i = 1; i < m; i++)
        if (seg[i].st <= ed)
            ed = max(seg[i].ed, ed);
        else {
            res -= ed - st + 1;
            st = seg[i].st, ed = seg[i].ed;
        }
    res -= ed - st + 1;
    cout << res << endl;
    return 0;
}