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

int main() {
	int n, m;
	cin >> n >> m;
	vector<int> trip(n+10);
	for(int i  = 0; i < m; i++) {
		int x, y;
		cin >> x >> y;
		trip[x]++;
		trip[y]--;
	}
	for(int i = 2; i < n; i++) {
		trip[i] += trip[i-1];
	}

	bool now = false;
	int ans = 0;

	for(int i = 2; i < n; i++) {
		if (trip[i-1] != 0 && trip[i] == 0) {
			ans++;
		}
	}



	if (trip[1] != 0) cout << ans << '\n';
	else cout << ans+1 << '\n';
	return 0;
}