#include <iostream>
using namespace std;

int l, m, cnt;
const int N = 1e6 + 10;
bool vis[N];

int main()
{
	cin >> l >> m;
	while(m --){
		int w, v;
		cin >> w >> v;
		for(int i = w; i <= v; i ++ ){
			vis[i] = true;
		}
	}
	for(int i = 1; i <= l; i ++ ){
		if(vis[i] == true) cnt ++;
	}
	cout << l - cnt + 1;
	return 0;
}