#include <bits/stdc++.h>
using namespace std;
vector<int> dy = {1, 0, -1, 0};
vector<int> dx = {0, 1, 0, -1};
int main(){
  int N, M;
  cin >> N >> M;
  vector<vector<int>> A(N, vector<int>(N, 0));
  for (int i = 0; i < M; i++){
    int h, w, c;
    cin >> h >> w >> c;
    h--;
    w--;
    A[h][w] = c;
  }
  priority_queue<tuple<long long, int, int, int>, vector<tuple<long long, int, int, int>>, greater<tuple<long long, int, int, int>>> pq;
  vector<vector<vector<long long>>> cost(N, vector<vector<long long>>(N, vector<long long>(2, -1)));
  pq.push(make_tuple(0, 0, 0, 0));
  while (!pq.empty()){
    long long sum = get<0>(pq.top());
    int y = get<1>(pq.top());
    int x = get<2>(pq.top());
    int u = get<3>(pq.top());
    pq.pop();
    if (cost[y][x][u] == -1){
      cost[y][x][u] = sum;
      for (int i = 0; i < 4; i++){
        int y2 = y + dy[i];
        int x2 = x + dx[i];
        if (0 <= y2 && y2 < N && 0 <= x2 && x2 < N){
          if (cost[y2][x2][u] == -1){
            pq.push(make_tuple(sum + A[y2][x2] + 1, y2, x2, u));
          }
          if (u == 0 && cost[y2][x2][1] == -1){
            pq.push(make_tuple(sum + 1, y2, x2, 1));
          }
        }
      }
    }
  }
  cout << cost[N - 1][N - 1][1] << endl;
}