#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using namespace std;
bool isPrimeNum(ll x) {
  if (x <= 1) {
    return false;
  }
  int n = (int)sqrt((double)x);
  for (int i = 2; i <= n; i++) {
    if (x % i == 0) {
      return false;
    }
  }
  return true;
}
ll myPow(ll x, ll n, ll m) {
  if (n == 0) return 1;
  if (n % 2 == 0)
    return myPow(x * x % m, n / 2, m);
  else
    return x * myPow(x, n - 1, m) % m;
}
constexpr ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
constexpr ll lcm(ll a, ll b) { return a * b / gcd(a, b); }
constexpr ll abs(ll a, ll b) {
  if (a >= b) return a - b;
  if (a < b) return b - a;
}
constexpr double dabs(double a, double b) {
  if (a >= b) return a - b;
  if (a < b) return b - a;
}
constexpr ll min(ll a, ll b) {
  if (a >= b) return b;
  if (a < b) return a;
}
constexpr ll max(ll a, ll b) {
  if (a >= b) return a;
  if (a < b) return b;
}
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
int dx8[8] = {1, 0, -1, 0, 1, -1, 1, -1};
int dy8[8] = {0, 1, 0, -1, 1, 1, -1, -1};
class UnionFind {
 public:
  vector<int> Parent;
  UnionFind(int N) { Parent = vector<int>(N, -1); }
  int root(int A) {
    if (Parent[A] < 0) return A;
    return Parent[A] = root(Parent[A]);
  }
  int size(int A) { return -Parent[root(A)]; }
  bool issame(int x, int y) { return root(x) == root(y); }
  bool connect(int A, int B) {
    A = root(A);
    B = root(B);
    if (A == B) {
      return false;
    }
    if (size(A) < size(B)) swap(A, B);
    Parent[A] += Parent[B];
    Parent[B] = A;
    return true;
  }
};
long long fac[510000], finv[510000], inv[510000];
void COMinit() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < 510000; i++) {
    fac[i] = fac[i - 1] * i % 1000000007;
    inv[i] = 1000000007 - inv[1000000007 % i] * (1000000007 / i) % 1000000007;
    finv[i] = finv[i - 1] * inv[i] % 1000000007;
  }
}
long long COM(int n, int k) {
  if (n < k) return 0;
  if (n < 0 || k < 0) return 0;
  return fac[n] * (finv[k] * finv[n - k] % 1000000007) % 1000000007;
}
long long modinv(long long a, long long m) {
  long long b = m, u = 1, v = 0;
  while (b) {
    long long t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0) u += m;
  return u;
}
string replaceAll(string &replacedStr, string from, string to) {
  unsigned int pos = replacedStr.find(from);
  int toLen = to.length();
  if (from.empty()) {
    return replacedStr;
  }
  while ((pos = replacedStr.find(from, pos)) != std::string::npos) {
    replacedStr.replace(pos, from.length(), to);
    pos += toLen;
  }
  return replacedStr;
}
void yn(bool flag) {
  if (flag) {
    cout << "Yes" << endl;
  } else {
    cout << "No" << endl;
  }
  return;
}
void YN(bool flag) {
  if (flag) {
    cout << "YES" << endl;
  } else {
    cout << "NO" << endl;
  }
  return;
}
std::vector<ll> enum_div(ll n) {
  std::vector<ll> ret;
  for (ll i = 1; i * i <= n; ++i) {
    if (n % i == 0) {
      ret.push_back(i);
      if (i != 1 && i * i != n) {
        ret.push_back(n / i);
      }
    }
  }
  ret.push_back(n);
  return ret;
}
void Ssort(int no, char *month[]) {
  int i, j;
  char *temp;
  for (i = 0; i < no; i++) {
    for (j = i + 1; j < no; j++) {
      if (strcmp((month[i]), (month[j])) > 0) {
        temp = *(month + i);
        *(month + i) = *(month + j);
        *(month + j) = temp;
      }
    }
  }
}
struct Edge {
  ll to;
  ll weight;
  Edge(int t, int w) : to(t), weight(w) {}
};
using Graph = vector<vector<Edge>>;
int main() {
  ll N, M;
  cin >> N >> M;
  Graph G(N);
  for (long long int i = (0); i <= (M - 1); i++) {
    int a, b, to;
    cin >> a >> b >> to;
    a--;
    b--;
    G[a].push_back(Edge(b, to));
  }
  ll dist[N];
  for (long long int i = (0); i <= (N - 1); i++) {
    dist[i] = 9223372036854775800 / 2;
  }
  dist[0] = 0;
  for (long long int i = (0); i <= (N - 1); i++) {
    ll ko = 0;
    if (G[i].empty()) continue;
    for (long long int j = (0); j <= (G[i].size() - 1); j++) {
      ko++;
      ll to = G[i][j].to;
      ll dis = G[i][j].weight;
      dist[to] = min(dist[to], dist[i] + dis);
    }
    if (ko > 0) {
      for (long long int j = (N - 2); j >= (0); j--) {
        dist[j] = min(dist[j], dist[j + 1]);
      }
    }
  }
  if (dist[N - 1] == 9223372036854775800 / 2) {
    dist[N - 1] = -1;
  }
  cout << dist[N - 1] << endl;
  return 0;
}
