#include <bits/stdc++.h>
using namespace std;
const int N = 1e4 + 1, M = 100;
int n, q;
bitset<N> sq[M];
vector<int> on[N];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> q;
  for (int x = 0, qwerty = M; x < qwerty; x++) sq[x][0] = 1;
  for (int x = 0, qwerty = q; x < qwerty; x++) {
    int l, r, v;
    cin >> l >> r >> v;
    l--;
    r--;
    if (l / M == r / M) {
      for (int i = l; i <= r; i++) on[i].push_back(v);
      continue;
    }
    for (int i = (l / M) + 1; i < r / M; i++) {
      sq[i] |= (sq[i] << v);
    }
    for (int i = l; i < M * ((l / M) + 1); i++) on[i].push_back(v);
    for (int i = M * (r / M); i <= r; i++) on[i].push_back(v);
  }
  bitset<N> ans;
  for (int x = 0, qwerty = n; x < qwerty; x++) {
    int pos = x / M;
    bitset<N> tmp = sq[pos];
    for (int v : on[x]) tmp |= tmp << v;
    ans |= tmp;
  }
  vector<int> aa;
  for (int x = 1, qwerty = n + 1; x < qwerty; x++)
    if (ans[x]) aa.push_back(x);
  cout << ((int)(aa).size()) << "\n";
  for (int x = 0, qwerty = ((int)(aa).size()); x < qwerty; x++)
    cout << aa[x] << " \n"[x + 1 == ((int)(aa).size())];
}
