#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];
    }

    x[0]=1;
    for (i = 1; i <= m; ++i)
    {
        if (i>1) x[i] += x[i-1];

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

    //if (x[1] == 0) ++db;

    cout << db;
}