#include <iostream>
#include <vector>

using namespace std;

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, m;
    cin >> n >> m;
    vector<int> vec(n + 2, 0);
    for (int i=0; i < m; i++) {
        int u, v;
        cin >> u >> v;
        vec[u]++; vec[v + 1]--;
    }
    int prev = -1;
    int cnt = 0;
    int ans = 0;
    for (int i=1; i <= n; i++) {
        cnt += vec[i];
        if (cnt == 0 && prev != 0) ans++;
        prev = cnt;
    }
    cout << ans << '\n';
    return 0;
}