#include <iostream>
#include <vector>
using namespace std;
#define speed cin.tie(0); ios::sync_with_stdio(0)

int main() {
    speed;
    
    int N, M;
    cin >> N >> M;
    vector<bool> line(N + 1);

    while (M--) {
        int E, V;
        cin >> E >> V;
        for (; E <= V; E++) {
            line[E] = 1;
        }
    }

    int result = 0;
    for (int i = 1; i <= N; i++) {
        if (!line[i]) {
            result++;
            while (i + 1 < line.size() && !line[i + 1]) i++;
        }
    }
    
    cout << result;
}