#include <bits/stdc++.h>
using namespace std;
long long POW(long long A, long long N, long long MOD) {
  if (N == 0) return 1 % MOD;
  if (N == 1) return A % MOD;
  long long tmp = POW(A, N / 2, MOD) % MOD;
  if (N % 2)
    return ((tmp * tmp) % MOD * A % MOD) % MOD;
  else
    return (tmp * tmp) % MOD;
}
long long MUL(long long A, long long B, long long MOD) {
  long long r = 0;
  while (B) {
    r = (r + (A * (B % 2) % MOD)) % MOD;
    A = (A + A) % MOD;
    B /= 2;
  }
  return r;
}
long long GCD(long long A, long long B) { return B == 0 ? A : GCD(B, A % B); }
int dx[] = {0, -1, 0, 1, 0};
int dy[] = {0, 0, 1, 0, -1};
template <class X, class Y>
bool minimize(X &x, const Y &y) {
  X eps = 1e-9;
  if (x > y + eps) {
    x = y;
    return true;
  } else
    return false;
}
template <class X, class Y>
bool maximize(X &x, const Y &y) {
  X eps = 1e-9;
  if (x + eps < y) {
    x = y;
    return true;
  } else
    return false;
}
template <class T>
T Abs(const T &x) {
  return (x < 0 ? -x : x);
}
const int MAXN = 1e4 + 105;
int N, Q;
struct DATA {
  int l, r, x;
} A[MAXN];
bool cmp(DATA &A, DATA &B) {
  if (A.r != B.r) return A.r < B.r;
  return A.l < B.l;
}
int pos[MAXN];
vector<int> RES;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  cin >> N >> Q;
  for (int i = (1), _b = (Q); i <= _b; ++i) {
    cin >> A[i].l >> A[i].r >> A[i].x;
  }
  sort(A + 1, A + 1 + Q, cmp);
  for (int i = (1), _b = (Q); i <= _b; ++i) {
    pos[0] = A[i].r;
    for (int j = (N), _a = (A[i].x); j >= _a; --j) {
      if (pos[j - A[i].x] >= A[i].l) maximize(pos[j], pos[j - A[i].x]);
    }
  }
  for (int i = (1), _b = (N); i <= _b; ++i)
    if (pos[i]) RES.push_back(i);
  cout << RES.size() << '\n';
  for (auto &val : RES) cout << val << ' ';
  return 0;
}
