#include <iostream>
#include <set>
#include <map>
#include <vector>
#include <string>
#include <algorithm>
#include <iomanip>
#include <math.h>
#include <limits.h>
using namespace std;
typedef long long int ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vint;


int n, q;
vint degrees;
vector<bool> can;

void add(int x) {
    //cerr << "add " << x << endl;
    vint nvec = degrees;
    for (int i = 0; i <= n; i++) {
        if (degrees[i] && i + x <= n) {
            nvec[i + x]++;
            can[i + x] = true;
        }
    }

    /*cerr << "nvec: ";
    for (auto it : nvec)
        cerr << it << " ";
    cerr << endl;*/

    degrees = nvec;
}

void remove(int x) {
    //cerr << "remove " << x << endl;
    vint nvec = degrees;
    for (int i = 0; i <= n; i++) {
        if (nvec[i] && i + x <= n)
            nvec[i + x]--;
    }

    /*cerr << "nvec: ";
    for (auto it : nvec)
        cerr << it << " ";
    cerr << endl;*/

    degrees = nvec;
}

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

    cin >> n >> q;
    vector<pii> vec;
    for (int i = 0; i < q; i++) {
        int l, r, x;
        cin >> l >> r >> x;
        l--; r--;
        vec.push_back({l, x});
        vec.push_back({r + 1, -x});
    }
    sort(vec.begin(), vec.end());
    degrees.resize(n + 1);
    can.resize(n + 1);
    degrees[0] = 1;

    for (auto it : vec) {
        if (it.second < 0)
            remove(-it.second);
        else
            add(it.second);
    }

    vint res;
    for (int i = 1; i <= n; i++) {
        if (can[i]) {
            res.push_back(i);
        }
    }

    cout << res.size() << endl;
    for (auto it : res)
        cout << it << " ";
    cout << endl;
}