// UUID: 59790dca-f9a5-44ff-8bbb-62d021d38c44
#include <bits/stdc++.h>
using namespace std;

int main() {
	int n, m;
	cin >> n >> m;

	vector<pair<int, int>> inters(m);

	for (int i = 0; i < m; i++) cin >> inters[i].first >> inters[i].second;

	sort(inters.begin(), inters.end());

	long long nemures = 0;
	int mostkezd = inters[0].first;
	int mostveg = inters[0].second;

	for(int i = 1; i < m; i++) {
		int kezd = inters[i].first;
		int veg = inters[i].second;

		if (kezd <= mostkezd) mostveg = max(mostveg, veg);
		else {
			nemures += mostveg - mostkezd;
			mostkezd = kezd;
			mostveg = veg;
		}
	}

	nemures += mostveg - mostkezd;

	long long total = (long long)n - 1;
	long long ures = total - nemures;

	cout << ures;
}