#include <bits/stdc++.h>
using namespace std;
using vi = vector<long long>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vvvvi = vector<vvvi>;
using vp = vector<pair<long long, long long>>;
using vvp = vector<vp>;
using vb = vector<bool>;
using vvb = vector<vb>;
const long long inf = 1001001001001001001;
const long long INF = 1001001001;
const long long mod = 1000000007;
const double eps = 1e-10;
template <class T>
bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
void out(T a) {
  cout << a << '\n';
}
template <class T>
void outp(T a) {
  cout << '(' << a.first << ',' << a.second << ')' << '\n';
}
template <class T>
void outvp(T v) {
  for (long long i = 0; i < (long long)(v.size()); i++)
    cout << '(' << v[i].first << ',' << v[i].second << ')';
  cout << '\n';
}
template <class T>
void outvvp(T v) {
  for (long long i = 0; i < (long long)(v.size()); i++) outvp(v[i]);
}
template <class T>
void outv(T v) {
  for (long long i = 0; i < (long long)(v.size()); i++) {
    if (i) cout << ' ';
    cout << v[i];
  }
  cout << '\n';
}
template <class T>
void outvv(T v) {
  for (long long i = 0; i < (long long)(v.size()); i++) outv(v[i]);
}
template <class T>
bool isin(T x, T l, T r) {
  return (l) <= (x) && (x) <= (r);
}
template <class T>
void yesno(T b) {
  if (b)
    out("yes");
  else
    out("no");
}
template <class T>
void YesNo(T b) {
  if (b)
    out("Yes");
  else
    out("No");
}
template <class T>
void YESNO(T b) {
  if (b)
    out("YES");
  else
    out("NO");
}
template <class T>
void noyes(T b) {
  if (b)
    out("no");
  else
    out("yes");
}
template <class T>
void NoYes(T b) {
  if (b)
    out("No");
  else
    out("Yes");
}
template <class T>
void NOYES(T b) {
  if (b)
    out("NO");
  else
    out("YES");
}
void outs(long long a, long long b) {
  if (a >= inf - 100)
    out(b);
  else
    out(a);
}
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long modpow(long long a, long long b) {
  long long res = 1;
  a %= mod;
  while (b) {
    if (b & 1) res = res * a % mod;
    a = a * a % mod;
    b >>= 1;
  }
  return res;
}
vi dijkstra(int from, vvp g) {
  vi dis(g.size(), inf);
  dis[from] = 0;
  priority_queue<pair<long long, long long>, vector<pair<long long, long long>>,
                 greater<pair<long long, long long>>>
      pq;
  pq.push(pair<long long, long long>(0, from));
  while (!pq.empty()) {
    auto t = pq.top();
    pq.pop();
    if (t.first != dis[t.second]) continue;
    for (auto x : g[t.second]) {
      if (chmin(dis[x.first], t.first + x.second))
        pq.push(pair<long long, long long>(dis[x.first], x.first));
    }
  }
  return dis;
}
int main() {
  long long n, m;
  cin >> n >> m;
  vvp g(n);
  for (long long i = 0; i < (long long)(n - 1); i++)
    g[i + 1].emplace_back(i, 0);
  for (long long i = 0; i < (long long)(m); i++) {
    long long l, r, c;
    cin >> l >> r >> c;
    g[l - 1].emplace_back(r - 1, c);
  }
  out(dijkstra(0, g)[n - 1]);
}
