#include <iostream>
#include <vector>

using namespace std;

int main()
{
	int N, K;
	cin >> N >> K;
	vector <int> x(N + 2, 0);

	int a, b;
	for (int i = 1; i <= K; ++i)
	{
		cin >> a >> b;
		++x[a];
		--x[b];
	}

	for (int i = 1; i <= N; ++i)
		x[i] += x[i - 1];

	x[N] = 1;
	int db = 0, a_db = 0;
	
	/*for (auto e : x) cout << e << ' ';
	cout << '\n';*/

	for (int i = 1; i <= N; ++i)
	{
		if (x[i] == 0) ++a_db;
		else
		{
			if (a_db != 0) db+=a_db;
			a_db = 0;
		}
	}

	cout << db << '\n';
	return 0;
}