#include<iostream>
using namespace std;
int main() {
	int l, m,count=0;
	int arr[100000] = { 0 };
	cin >> l >> m;
	for (int i = 0; i <= l; i++) {
		arr[i] = 1;
	}
	for (int j = 0; j < m; j++) {
		int u = 0, v = 0;
		cin >> u >> v;
		for (int i = u - 1; i < v; i++) {
			arr[i] = 0;
		}
	}
	for (int i = 0; i <= l; i++) {
		if (arr[i] == 1) {
			count++;
		}
	}
	cout << count;
	return 0;
}