#include <bits/stdc++.h>

using namespace std;

int main()
{
    int n, a;
    cin >> n >> a;
    vector<int> sor (n);
    vector<int> valt (n);
    for (int i = 0; i < a; i++) {
        int fel, le;
        cin >> fel >> le;
        valt[fel - 1] += 1;
        valt[le - 1] -= 1;
    }
    int jl = 0;
    for (int i = 0; i < n; i++) {
        jl += valt[i];
        sor[i] = jl;
        //cout << sor[i] << " ";
    }
    int ures = 0;
    bool nincs = true;
    for (int i = 0; i < n; i++) {
        if (sor[i] == 0 && nincs == false) {
            ures += 1;
            nincs = true;
        } else if (sor[i] != 0 && nincs == true) {
        nincs = false;
        }
    }
    cout << ures;
}