#include <bits/stdc++.h>

using namespace std;



int main()
{
    int n, m;
    cin >> n >> m;
    vector<int> plusz(n+1, 0);
    for (int i=0; i<m; i++) {
        int x, y;
        cin>>x>>y;
        plusz[x]++;
        plusz[y+1]--;
    }

    int vege=0, epp=0;
    for(int i=1; i<=n; i++) {

        epp+=plusz[i];
        if (epp==0) {
            vege++;
        }
    }
    cout << vege << "\n";
    return 0;
}