#include <bits/stdc++.h>
using namespace std;
long long int INF = 3e18;
const long long fact_table = 5000000;
double Pi = 3.1415926535897932384626;
vector<pair<long long, long long> > tree[500010];
priority_queue<long long> pql;
priority_queue<pair<long long, long long> > pqp;
priority_queue<long long, vector<long long>, greater<long long> > pqls;
priority_queue<pair<long long, long long>, vector<pair<long long, long long> >,
               greater<pair<long long, long long> > >
    pqps;
int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
int dy[8] = {0, 1, 0, -1, 1, -1, -1, 1};
char dir[] = "DRUL";
long long mod = 998244353;
long long rui(long long number1, long long number2) {
  if (number2 == 0) {
    return 1;
  } else {
    long long number3 = rui(number1, number2 / 2);
    number3 *= number3;
    number3 %= mod;
    if (number2 % 2 == 1) {
      number3 *= number1;
      number3 %= mod;
    }
    return number3;
  }
}
long long gcd(long long number1, long long number2) {
  if (number1 > number2) {
    swap(number1, number2);
  }
  if (number1 == 0 || number1 == number2) {
    return number2;
  } else {
    return gcd(number2 % number1, number1);
  }
}
void YES(bool condition) {
  if (condition) {
    cout << "YES"
         << "\n";
    ;
  } else {
    cout << "NO"
         << "\n";
    ;
  }
  return;
}
void Yes(bool condition) {
  if (condition) {
    cout << "Yes"
         << "\n";
    ;
  } else {
    cout << "No"
         << "\n";
    ;
  }
  return;
}
long long n, m, num, sum, a, b, c, d, e, g, h, w, i, j, q, r, l;
long long k, idx, ans;
long long x[500005], y[500005], z[500005];
bool used[500005];
pair<long long, long long> table[500005];
long long cost[500005];
char s[500005];
int main() {
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    cin >> l >> r >> c;
    tree[l].push_back(pair<long long, long long>(r, c));
  }
  for (int i = 1; i <= n - 1; i++) {
    tree[i + 1].push_back(pair<long long, long long>(i, 0));
  }
  pqps.push(pair<long long, long long>(0, 1));
  for (int i = 1; i <= n; i++) {
    cost[i] = INF;
  }
  cost[1] = 0;
  while (!pqps.empty()) {
    pair<long long, long long> p = pqps.top();
    pqps.pop();
    long long v = p.second;
    long long nowcost = p.first;
    if (nowcost > cost[v]) continue;
    for (int i = 0; i < tree[v].size(); i++) {
      long long nv = tree[v][i].first;
      long long newcost = cost[v] + tree[v][i].second;
      if (cost[nv] > newcost) {
        cost[nv] = newcost;
        pqps.push(pair<long long, long long>(newcost, nv));
      }
    }
  }
  for (int i = 1; i <= n; i++) {
  }
  cout << cost[n] << "\n";
  ;
  return 0;
}
