#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 1000000007;
// constexpr int MOD = 998244353;
constexpr int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
constexpr int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  int n, m; cin >> n >> m;
  vector c(n, vector(n, 1));
  while (m--) {
    int h, w, ci; cin >> h >> w >> ci; --h; --w;
    c[h][w] += ci;
  }
  vector dist(n, vector(n, vector(2, LINF)));
  dist[0][0][false] = 0;
  using P = pair<ll, tuple<int, int, bool>>;
  priority_queue<P, vector<P>, greater<P>> que;
  que.emplace(0, make_tuple(0, 0, false));
  while (!que.empty()) {
    auto [cost, node] = que.top(); que.pop();
    auto [i, j, b] = node;
    if (cost > dist[i][j][b]) continue;
    REP(k, 4) {
      int y = i + dy[k], x = j + dx[k];
      if (0 <= y && y < n && 0 <= x && x < n) {
        int nx = cost + c[y][x];
        if (nx < dist[y][x][b]) {
          dist[y][x][b] = nx;
          que.emplace(nx, make_tuple(y, x, b));
        }
        if (c[y][x] > 1 && !b && cost + 1 < dist[y][x][true]) {
          dist[y][x][true] = cost + 1;
          que.emplace(cost + 1, make_tuple(y, x, true));
        }
      }
    }
  }
  cout << *min_element(ALL(dist[n - 1][n - 1])) << '\n';
  return 0;
}