// UUID: 8ad89f40-7129-4ece-9559-c03cb76c86d6
#include <bits/stdc++.h>
using namespace std;

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


	vector<int> diffs(n+1, 0);
	for (int i=0;i<m;i++){
		int start, end;
		cin >> start >> end;
		diffs[start]++;
		diffs[end]--;
	}

	// for(int d:diffs){
	// 	cout << d << " ";
	// }
	// cout << "\n";

	if(m==1){
		cout << (diffs[1] == 0 ? 1 : 0);
		return 0;
	}

	vector<int> totals(n+1, 0);
	
	totals[1] = diffs[1];
	
	for(int i=2;i<=n;i++){
		totals[i] = totals[i-1] + diffs[i];
	}
	// for(int t:totals){
	// 	cout << t << " ";
	// }
	// cout << "\n";

	int empty_section_count = 0;

	for(int i=0;i<=n;i++){
		if (totals[i]==0){
			empty_section_count++;
			while(i<n && totals[i]==0){
				i++;
			}
		}
	}

	cout << (totals[1] == 0 ? empty_section_count: empty_section_count - 1);
}