// Áruszállítás üres szakaszai.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include <iostream>
#include <vector>

using namespace std;

long long n, m, i, a, b, akt, db;
bool elozo;

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);

    cin >> m >> n;

    vector <long long> x(m + 1);

    for (i = 1; i <= n; ++i)
    {
        cin >> a >> b;
        ++x[a];
        --x[b+1];
    }

    for (i = 1; i <= m; ++i)
    {
        x[i] += x[i - 1];
    }
    
    for (i = 1; i <= m; ++i)
    {
        if (x[i] == 0 && x[i-1]!=0)
        {
            ++db;
        }
    }
    if (x[1] == 0) ++db;

    cout << db;
}

// Run program: Ctrl + F5 or Debug > Start Without Debugging menu
// Debug program: F5 or Debug > Start Debugging menu

// Tips for Getting Started: 
//   1. Use the Solution Explorer window to add/manage files
//   2. Use the Team Explorer window to connect to source control
//   3. Use the Output window to see build output and other messages
//   4. Use the Error List window to view errors
//   5. Go to Project > Add New Item to create new code files, or Project > Add Existing Item to add existing code files to the project
//   6. In the future, to open this project again, go to File > Open > Project and select the .sln file