#include <bits/stdc++.h>

using namespace std;

using ll = long long;

constexpr char newl = '\n';
constexpr int dh[] = {1, -1, 0, 0};
constexpr int dw[] = {0, 0, 1, -1};

struct State {
    int at;
    ll cost;
    bool used;
    //int prev;
    State(int at, ll cost, bool used) : at(at), cost(cost), used(used) {}
    bool operator>(const State& s) const {
        return cost > s.cost;
    }
};

struct Edge {
    int to;
    ll cost;
    Edge(int to, ll cost) : to(to), cost(cost) {}
};

using Graph = vector< vector<Edge> >; //隣接リスト

const ll INF = 1e15;
//const int NONE = -1;

//sは始点、mincは最短経路のコスト、prevsは最短経路をたどる際の前の頂点
void dijkstra(int s, const Graph& graph, vector< vector<ll> >& minc){
    minc.assign(2, vector<ll>(graph.size(), INF));

    priority_queue<State, vector<State>, greater<State> > pq;
    pq.emplace(s, 0, false);
    minc[false][s] = 0;

    while(!pq.empty()) {
        State cur = pq.top();
        pq.pop();
        if (minc[cur.used][cur.at] < cur.cost) continue;

        for(const Edge& e : graph[cur.at]) {
            if (!cur.used) {
                ll cost = cur.cost + 1;
                if (minc[true][e.to] > cost) {
                    minc[true][e.to] = cost;
                    pq.emplace(e.to, cost, true);
                }
            }

            ll cost = cur.cost + e.cost;
            if (minc[cur.used][e.to] <= cost) continue;
            minc[cur.used][e.to] = cost;
            pq.emplace(e.to, cost, cur.used);
        }
    }
}

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    int n, m;
    cin >> n >> m;

    vector< vector<ll> > memo(n, vector<ll>(n, 0));
    for (int i = 0; i < m; i++) {
        int h, w;
        ll c;
        cin >> h >> w >> c;
        --h; --w;
        memo[h][w] = c;
    }

    Graph g(n * n);
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            for (int k = 0; k < 4; k++) {
                int nh = i + dh[k], nw = j + dw[k];
                if (nh < 0 || nh >= n || nw < 0 || nw >= n) continue;
                g[i * n + j].emplace_back(nh * n + nw, memo[nh][nw] + 1);
            }
        }
    }

    vector< vector<ll> > minc;
    dijkstra(0, g, minc);
    int goal = (n - 1) * n + (n - 1);
    cout << min(minc[0][goal], minc[1][goal]) << newl; 

    return 0;
}