#include <bits/stdc++.h>
using namespace std;
template <typename A, typename B>
string to_string(pair<A, B> p);
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);
string to_string(const string& s) { return '"' + s + '"'; }
string to_string(const char* s) { return to_string((string)s); }
string to_string(bool b) { return (b ? "true" : "false"); }
string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}
template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto& x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ")";
}
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
const int maxn = 1e4 + 5;
vector<int> b[maxn << 2];
void update(int L, int R, int val, int l, int r, int rt) {
  if (L <= l && r <= R) {
    b[rt].push_back(val);
    return;
  }
  int m = l + r >> 1;
  if (L <= m) {
    update(L, R, val, l, m, rt << 1);
  }
  if (R > m) {
    update(L, R, val, m + 1, r, rt << 1 | 1);
  }
}
bitset<maxn> ans;
void work(bitset<maxn> now, int l, int r, int rt) {
  vector<int>& it = b[rt];
  for (int i = 0; i < it.size(); i++) {
    now |= (now << it[i]);
  }
  if (l == r) {
    ans |= now;
    return;
  }
  int m = l + r >> 1;
  work(now, l, m, rt << 1);
  work(now, m + 1, r, rt << 1 | 1);
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, q;
  cin >> n >> q;
  for (int i = 1; i <= q; i++) {
    int l, r, w;
    cin >> l >> r >> w;
    update(l, r, w, 1, n, 1);
  }
  bitset<maxn> now;
  now[0] = 1;
  work(now, 1, n, 1);
  int res = 0;
  for (int i = 1; i <= n; i++) {
    if (ans[i]) {
      res++;
    }
  }
  cout << res << endl;
  for (int i = 1; i <= n; i++) {
    if (ans[i]) {
      cout << i << ' ';
    }
  }
  cout << endl;
}
