#include <iostream>
#include <vector>
#define ll long long 

using namespace std;

ll n, m, i, j, a, b;

int main()
{
    ios::sync_with_stdio(false);
    cin >> n >> m;
    vector <ll> x(2 * n + 2);
    for (i = 1; i <= m; ++i)
    {
        cin >> a >> b;
        x[a * 2]++;
        x[b * 2]--;
    }
    n = 2 * n;
    ll db = 0;
    x[n + 1] = 100000000;
    for (i = 3; i <= n; ++i)
    {
        x[i] += x[i - 1];
        if (x[i] != 0 && x[i - 1] == 0) db++;
    }
    if (x[n - 1] == 0 && x[n] == 0) db++;
    cout << db << "\n";

    return 0;
}