#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-8;
const int MOD = 1000000007;
// const int MOD = 998244353;
const int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
const int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  }
} iosetup;

template <typename Monoid>
struct RMQandRAQ {
  RMQandRAQ(int sz, const Monoid UNITY, const Monoid DEFAULT = 0) : UNITY(UNITY), DEFAULT(DEFAULT) {
    init(sz);
    dat.assign((n << 1) - 1, DEFAULT);
  }

  RMQandRAQ(const vector<Monoid> &a, const Monoid UNITY, const Monoid DEFAULT = 0) : UNITY(UNITY), DEFAULT(DEFAULT) {
    int a_sz = a.size();
    init(a_sz);
    dat.resize((n << 1) - 1);
    REP(i, a_sz) dat[n - 1 + i] = a[i];
    for (int i = n - 2; i >= 0; --i) dat[i] = min(dat[(i << 1) + 1], dat[(i << 1) + 2]);
  }

  void add(int a, int b, Monoid val) { add(a, b, val, 0, 0, n); }

  Monoid query(int a, int b) { return query(a, b, 0, 0, n); }

  Monoid operator[](const int idx) { return query(idx, idx + 1); }

  int find(int a, int b, Monoid val) { return find(a, b, val, 0, 0, n); }

private:
  int n = 1;
  const Monoid UNITY, DEFAULT;
  vector<Monoid> dat, lazy;

  void init(int sz) {
    while (n < sz) n <<= 1;
    lazy.assign((n << 1) - 1, DEFAULT);
  }

  inline void evaluate(int node) {
    if (lazy[node] != DEFAULT) {
      dat[node] += lazy[node];
      if (node < n - 1) {
        lazy[(node << 1) + 1] += lazy[node];
        lazy[(node << 1) + 2] += lazy[node];
      }
      lazy[node] = DEFAULT;
    }
  }

  void add(int a, int b, Monoid val, int node, int left, int right) {
    evaluate(node);
    if (right <= a || b <= left) return;
    if (a <= left && right <= b) {
      lazy[node] += val;
      evaluate(node);
    } else {
      add(a, b, val, (node << 1) + 1, left, (left + right) >> 1);
      add(a, b, val, (node << 1) + 2, (left + right) >> 1, right);
      dat[node] = min(dat[(node << 1) + 1], dat[(node << 1) + 2]);
    }
  }

  Monoid query(int a, int b, int node, int left, int right) {
    evaluate(node);
    if (right <= a || b <= left) return UNITY;
    if (a <= left && right <= b) return dat[node];
    return min(query(a, b, (node << 1) + 1, left, (left + right) >> 1), query(a, b, (node << 1) + 2, (left + right) >> 1, right));
  }

  int find(int a, int b, Monoid val, int node, int left, int right) {
    evaluate(node);
    if (dat[node] > val || right <= a || b <= left) return -1;
    if (right - left == 1) return node - (n - 1);
    int res_l = find(a, b, val, (node << 1) + 1, left, (left + right) >> 1);
    if (res_l != -1) return res_l;
    return find(a, b, val, (node << 1) + 2, (left + right) >> 1, right);
  }
};

int main() {
  int n, m; cin >> n >> m;
  ll ans = 0;
  vector<vector<pair<int, int> > > score(n + 2);
  while (m--) {
    int l, r, a; cin >> l >> r >> a;
    ans += a;
    score[r].emplace_back(l, a);
  }
  RMQandRAQ<ll> dp(n + 2, LINF);
  FOR(i, 1, n + 2) {
    dp.add(i, i + 1, dp.query(0, i));
    for (auto pr : score[i]) {
      int l, a; tie(l, a) = pr;
      dp.add(0, l, a);
    }
    // REP(j, n + 2) cout << dp[j] << " \n"[j + 1 == n + 2];
  }
  cout << ans - dp[n + 1] << '\n';
  return 0;
}


Measured memory_bytes: 19456