#include <iostream>
using namespace std;

int main()
{
    int l;
    cin >> l;
    int trees[10000];
    int m;
    cin >> m;
    int a, b;
    for (int i = 0; i < m; i++)
    {
        cin >> a >> b;
        for (int j = a; j < b; a++)
        {
            trees[j] = 0;
        }
    }
    int num = m;
    for (int i = 0; i < l; i++)
    {
        if (trees[i] == 0)
        {
            num--;
        }
    }
    cout << num;
}