#include <bits/stdc++.h>
using namespace std;
char string_in_buffer[(int)260];
void fast_scan(int &first) { scanf("%d", &first); }
void fast_scan(long long &first) { scanf("%lld", &first); }
void fast_scan(unsigned long long &first) { scanf("%llu", &first); }
void fast_scan(double &first) { scanf("%lf", &first); }
void fast_scan(long double &first) { scanf("%Lf", &first); }
void fast_scan(char &first) {
  scanf("%c", &first);
  if (first == '\n') {
    fast_scan(first);
  }
}
void fast_scan(string &first) {
  scanf("%s", string_in_buffer);
  first = string(string_in_buffer);
}
template <class TFirst, class TSecond>
void fast_scan(pair<TFirst, TSecond> &p) {
  fast_scan(p.first);
  fast_scan(p.second);
}
template <class T>
void fast_scan(vector<T> &v) {
  for (auto &first : v) fast_scan(first);
}
void fast_print(const int &first) { printf("%d", first); }
void fast_print(const long long &first) { printf("%lld", first); }
void fast_print(const unsigned long long &first) { printf("%llu", first); }
void fast_print(const double &first) { printf("%.15lf", first); }
void fast_print(const long double &first) { printf("%.15Lf", first); }
void fast_print(const char &first) { printf("%c", first); };
void fast_print(const string &first) { printf("%s", first.c_str()); }
void fast_print(const char v[]) { fast_print((string)v); }
template <class TFirst, class TSecond>
void fast_print(const pair<TFirst, TSecond> &p) {
  fast_print(p.first);
  fast_print(' ');
  fast_print(p.second);
}
template <class T>
void fast_print(const vector<T> &v) {
  if (v.empty()) return;
  fast_print(v[0]);
  for (int i = 1; i < v.size(); i++) {
    fast_print(' ');
    fast_print(v[i]);
  }
}
template <class T>
void fast_print(const vector<vector<T>> &v) {
  if (v.empty()) return;
  fast_print(v[0]);
  for (int i = 1; i < v.size(); i++) {
    fast_print('\n');
    fast_print(v[i]);
  }
}
template <class T>
void fast_print(const T &v) {
  for (const auto &first : v) {
    fast_print(first);
    fast_print(' ');
  }
}
using namespace std;
namespace smart_io {
string print_start = "";
string sep = " ";
bool first_print = false;
void precall_print() {
  fast_print(print_start);
  print_start = "\n";
  first_print = true;
}
void _print(deque<string>) {}
template <class T, class... Args>
void _print(deque<string> names, T kek, Args... args) {
  if (!first_print) {
    fast_print("\n");
  } else {
    first_print = false;
  }
  fast_print(names.front());
  fast_print(" = ");
  fast_print(kek);
  names.pop_front();
  _print(names, args...);
}
}  // namespace smart_io
template <class T>
ostream &operator,(ostream &os, const T &object) {
  if (!smart_io::first_print) {
    fast_print(smart_io::sep);
  } else {
    smart_io::first_print = false;
  }
  fast_print(object);
  return os;
}
template <class T>
istream &operator,(istream &is, T &object) {
  fast_scan(object);
  return is;
}
namespace typedefs {}
namespace numbers_operation {
template <class T>
T floor_mod(T a, T b) {
  if (a % b == 0) return 0;
  if (a >= 0 && b >= 0) return a % b;
  if (a <= 0 && b <= 0) return a % b;
  return abs(b) - (abs(a) % abs(b));
}
}  // namespace numbers_operation
using namespace numbers_operation;
using namespace typedefs;
const int N = 1e4 + 1;
bitset<N> rez;
int n, q;
struct Event {
  int first;
  int id;
  int type;
  int pair_id = -1;
  int d = -1;
  Event() {}
  Event(int _x, int _id, int _d, int _type) {
    first = _x;
    id = _id;
    type = _type;
    d = _d;
  }
};
vector<Event> events;
void go(int l, int r, bitset<N> cur) {
  if (l >= r) return;
  if (l + 1 == r) {
    if (events[l].type == 1) {
      rez = (rez | cur);
    }
  } else {
    int mid = (l + r) / 2;
    {
      bitset<N> sub = cur;
      for (int i = mid; i < r; i++) {
        if (events[i].type == 2) {
          if (events[i].pair_id < l) {
            sub = (sub | (sub << events[i].d));
          }
        }
      }
      go(l, mid, sub);
    }
    {
      bitset<N> sub = cur;
      for (int i = l; i < mid; i++) {
        if (events[i].type == 0) {
          if (events[i].pair_id >= r) {
            sub = (sub | (sub << events[i].d));
          }
        }
      }
      go(mid, r, sub);
    }
  }
}
signed main(signed argc, char *argv[]) {
  { cin, n, q; }
  {
    for (int i = 0; i < (q); i++) {
      int l, r, first;
      cin, l, r, first;
      events.emplace_back(l, i, first, 0);
      events.emplace_back(r, i, first, 2);
    }
  }
  {
    for (int i = 1; i <= n; i++) {
      events.emplace_back(i, -1, -1, 1);
    }
  }
  {
    sort(events.begin(), events.end(), [](Event a, Event b) {
      if (a.first < b.first) return true;
      if (a.first > b.first) return false;
      return a.type < b.type;
    });
  }
  {
    vector<vector<int>> at(3, vector<int>(q));
    for (int i = 0; i < (((int)events.size())); i++) {
      Event &e = events[i];
      if (e.id != -1) {
        at[e.type][e.id] = i;
      }
    }
    for (int i = 0; i < (((int)events.size())); i++) {
      Event &e = events[i];
      if (e.id != -1) {
        e.pair_id = at[e.type ^ 2][e.id];
      }
    }
  }
  {} { go(0, ((int)events.size()), 1); }
  {
    vector<int> final;
    for (int i = 1; i <= n; i++) {
      if (rez[i]) {
        final.push_back(i);
      }
    }
    smart_io::precall_print();
    cout, ((int) final.size());
    smart_io::precall_print();
    cout, final;
  }
}
