#include <bits/stdc++.h>
using namespace std;
template <typename Monoid, typename OperatorMonoid = Monoid>
struct LazySegmentTree {
  using F = function<Monoid(Monoid, Monoid)>;
  using G = function<Monoid(Monoid, OperatorMonoid)>;
  using H = function<OperatorMonoid(OperatorMonoid, OperatorMonoid)>;
  long sz, height;
  vector<Monoid> data;
  vector<OperatorMonoid> lazy;
  const F f;
  const G g;
  const H h;
  const Monoid M1;
  const OperatorMonoid OM0;
  LazySegmentTree(long n, const F f, const G g, const H h, const Monoid &M1,
                  const OperatorMonoid OM0)
      : f(f), g(g), h(h), M1(M1), OM0(OM0) {
    sz = 1;
    height = 0;
    while (sz < n) sz <<= 1, height++;
    data.assign(2 * sz, M1);
    lazy.assign(2 * sz, OM0);
  }
  void set(long k, const Monoid &x) { data[k + sz] = x; }
  void build() {
    for (int k = sz - 1; k > 0; k--) {
      data[k] = f(data[2 * k + 0], data[2 * k + 1]);
    }
  }
  inline void propagate(long k) {
    if (lazy[k] != OM0) {
      lazy[2 * k + 0] = h(lazy[2 * k + 0], lazy[k]);
      lazy[2 * k + 1] = h(lazy[2 * k + 1], lazy[k]);
      data[k] = reflect(k);
      lazy[k] = OM0;
    }
  }
  inline Monoid reflect(long k) {
    return lazy[k] == OM0 ? data[k] : g(data[k], lazy[k]);
  }
  inline void recalc(long k) {
    while (k >>= 1) data[k] = f(reflect(2 * k + 0), reflect(2 * k + 1));
  }
  inline void thrust(long k) {
    for (int i = height; i > 0; i--) propagate(k >> i);
  }
  void update(long a, long b, const OperatorMonoid &x) {
    thrust(a += sz);
    thrust(b += sz - 1);
    for (int l = a, r = b + 1; l < r; l >>= 1, r >>= 1) {
      if (l & 1) lazy[l] = h(lazy[l], x), ++l;
      if (r & 1) --r, lazy[r] = h(lazy[r], x);
    }
    recalc(a);
    recalc(b);
  }
  Monoid query(long a, long b) {
    thrust(a += sz);
    thrust(b += sz - 1);
    Monoid L = M1, R = M1;
    for (int l = a, r = b + 1; l < r; l >>= 1, r >>= 1) {
      if (l & 1) L = f(L, reflect(l++));
      if (r & 1) R = f(reflect(--r), R);
    }
    return f(L, R);
  }
  Monoid operator[](const int &k) { return query(k, k + 1); }
  template <typename C>
  long find_subtree(long a, const C &check, Monoid &M, bool type) {
    while (a < sz) {
      propagate(a);
      Monoid nxt =
          type ? f(reflect(2 * a + type), M) : f(M, reflect(2 * a + type));
      if (check(nxt))
        a = 2 * a + type;
      else
        M = nxt, a = 2 * a + 1 - type;
    }
    return a - sz;
  }
  template <typename C>
  long find_first(long a, const C &check) {
    Monoid L = M1;
    if (a <= 0) {
      if (check(f(L, reflect(1)))) return find_subtree(1, check, L, false);
      return -1;
    }
    thrust(a + sz);
    long b = sz;
    for (a += sz, b += sz; a < b; a >>= 1, b >>= 1) {
      if (a & 1) {
        Monoid nxt = f(L, reflect(a));
        if (check(nxt)) return find_subtree(a, check, L, false);
        L = nxt;
        ++a;
      }
    }
    return -1;
  }
  template <typename C>
  long find_last(long b, const C &check) {
    Monoid R = M1;
    if (b >= sz) {
      if (check(f(reflect(1), R))) return find_subtree(1, check, R, true);
      return -1;
    }
    thrust(b + sz - 1);
    long a = sz;
    for (b += sz; a < b; a >>= 1, b >>= 1) {
      if (b & 1) {
        Monoid nxt = f(reflect(--b), R);
        if (check(nxt)) return find_subtree(b, check, R, true);
        R = nxt;
      }
    }
    return -1;
  }
};
int main() {
  int n, m;
  cin >> n >> m;
  pair<pair<int, int>, long> pr[m];
  for (int i = 0; i < m; i++) {
    cin >> pr[i].first.second >> pr[i].first.first >> pr[i].second;
    pr[i].first.second--;
    pr[i].first.first--;
  }
  sort(pr, pr + m);
  LazySegmentTree<long> seg(
      n, [](long a, long b) { return min(a, b); },
      [](long a, long b) { return min(a, b); },
      [](long a, long b) { return min(a, b); }, INT_MAX, INT_MAX);
  seg.update(0, 1, 0);
  for (int i = 0; i < m; i++) {
    long long tmp = seg.query(pr[i].first.second, 1 + pr[i].first.first);
    seg.update(pr[i].first.second, 1 + pr[i].first.first, tmp + pr[i].second);
  }
  long tm = -1;
  cout << max(seg.query(n - 1, n), tm) << endl;
}
