#include <iostream>
#include <vector>
#include <algorithm>
#define rep(i, l, n) for (int i = (l); i < (n); i++)
#define all(x) x.begin(), x.end()
using namespace std;
template <class T>
using V = vector<T>;
template <class T>
using VV = V<V<T> >;


int main(void) {
	int n, m;	cin >> n >> m;
	VV<int> plan(m);
	rep(i, 0, m) {
		int a, b;	cin >> a >> b;
		plan[i] = { a,b };
	}
	sort(all(plan), [](auto& l, auto& r) {
		return (l[1] < r[1]);
	});

	int now = 0;
	int ans = 2 * (n - 1);
	for (auto& x : plan) {
		if (now > x[0]) {
			continue;
		}
		now = x[1];
		ans--;
	}

	cout << ans << endl;
	return 0;
}