#include <iostream>

using namespace std;
int aru[1000001]={ 0 };
int main()
{
    int n, m, db=0;
    cin >> n >> m;
    int x, y;
    aru[n] = 1;

    for (int i = 1; i <= m; i++) {
        cin >> x >> y;
        for(int j=x;j<n;j++)
        {
            aru[i]++;
        }
    }
    for (int i = 1; i <= n; i++) {
        if (aru[i]==0 and aru[i+1]==0) {
            i++;db++;
        }
    }
    cout << db;
    return 0;
}