//██████╗ ██╗   ██╗██╗      ██████╗ ███████╗
//██╔══██╗██║   ██║██║      ██╔══██╗██╔════╝
//██████╔╝██║   ██║██║█████╗██║  ██║█████╗
//██╔══██╗██║   ██║██║╚════╝██║  ██║██╔══╝
//██║  ██║╚██████╔╝██║      ██████╔╝███████╗
//╚═╝  ╚═╝ ╚═════╝ ╚═╝      ╚═════╝ ╚══════╝
#include <bits/stdc++.h>
#include <set>
using namespace std;

#define fst first
#define snd second
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define eb emplace_back

#define all(v) (v).begin(), (v).end()
#define sz(v) ((int)(v).size())
#define sqr(x) ((x) * (x))

#define ADD_OPERATORS_IN(T, COMP) \
    bool operator < (const T& ot) const { return COMP(ot) == -1; } \
    bool operator > (const T& ot) const { return COMP(ot) == 1; } \
    bool operator == (const T& ot) const { return COMP(ot) == 0; } \
    bool operator != (const T& ot) const { return COMP(ot) != 0; }

#define ADD_OPERATORS_OUT(T, COMP) \
    bool operator < (const T& a, const T& b) const { return COMP(a, b) == -1; } \
    bool operator > (const T& a, const T& b) const { return COMP(a, b) == 1; } \
    bool operator == (const T& a, const T&b) const { return COMP(a, b) == 0; } \
    bool operator != (const T& a, const T&b) const { return COMP(a, b) != 0; }


typedef long long ll;
typedef long double ld;
typedef pair <int, int> pii;
typedef pair <ll, ll> pll;

mt19937 mt_rand(chrono::system_clock::now().time_since_epoch().count());

template<typename T1, typename T2> inline bool upmax(T1& a, T2 b) { if (a < b) { a = b; return 1; } return 0; }
template<typename T1, typename T2> inline bool upmin(T1& a, T2 b) { if (b < a) { a = b; return 1; } return 0; }

const int maxn = (int) 10002;
const int base = 2147483647;

const ld PI = acos(-1.);

#define next ajksdslk

int n, q;
bitset<maxn> a, ans;

int main() {
    scanf ("%d%d", &n, &q);
    a.set(0);
    ans.set(0);
    vector<pair<int, int>> event;

    for (int i = 1; i <= q; i ++) {
        int l, r, x;
        scanf ("%d%d%d", &l, &r, &x);
        event.eb(l, x);
        event.eb(r + 1, -x);
    }

    sort(all(event));
    int ptr = 0;
    for (int i = 1; i <= n; i ++) {
        while (ptr < event.size() && event[ptr].first == i) {
            int x = event[ptr].second;
            if (x < 0) {
                x = abs(x);
                a = (a >> x) & a;
            } else {
                a = (a << x) | a;
            }
            ptr ++;
        }
        ans |= a;
    }
    vector<int> vec;
    for (int i = 1; i <= n; i ++) {
        if (ans[i]) {
            vec.pb(i);
        }
    }
    cout << vec.size() << '\n';
    for (int v : vec) {
        cout << v << " ";
    }
    return 0;

}