#include <bits/stdc++.h>

using namespace std;

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(0);

    int n, m, a, b;
    cin >> n >> m;

    vector<int> csomag(n, 0);
    while(m--)
    {
        cin >> a >> b;
        csomag[a-1]++;
        csomag[b-1]--;
    }
    int uresszam = 0, t = 0, j = n-1;


    bool prev_ures = false;
    bool ures = false;

    for(int i = 0; i < n; i++)
    {
        t += csomag[i];

        prev_ures = ures;
        ures = t == 0;

        uresszam += ures && i != j && prev_ures != ures;
    }

    cout << uresszam << "\n";

    return 0;
}