#include <algorithm>
#include <atcoder/all>
#include <bitset>
#include <cassert>
#include <cmath>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n) - 1; i >= 0; i--)
#define repk(i, k, n) for (int i = k; i < (int)(n); i++)
#define all(v) v.begin(), v.end()
#define mod1 1000000007
#define mod2 998244353
#define mod3 100000007
#define vi vector<int>
#define vs vector<string>
#define vc vector<char>
#define vl vector<ll>
#define vb vector<bool>
#define vvi vector<vector<int>>
#define vvc vector<vector<char>>
#define vvl vector<vector<ll>>
#define vvb vector<vector<bool>>
#define vvvi vector<vector<vector<int>>>
#define vvvl vector<vector<vector<ll>>>
#define pii pair<int, int>
#define pil pair<int, ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define vpii vector<pair<int, int>>
#define vpll vector<pair<ll, ll>>
#define vvpii vector<vector<pair<int, int>>>
#define vvpll vector<vector<pair<ll, ll>>>

template <typename T>
void debug(T e) {
    cerr << e << endl;
}

template <typename T>
void debug(vector<T> &v) {
    rep(i, v.size()) { cerr << v[i] << " "; }
    cerr << endl;
}

template <typename T>
void debug(vector<vector<T>> &v) {
    rep(i, v.size()) {
        rep(j, v[i].size()) { cerr << v[i][j] << " "; }
        cerr << endl;
    }
}

template <typename T>
void debug(vector<pair<T, T>> &v) {
    rep(i, v.size()) { cerr << v[i].first << " " << v[i].second << endl; }
}

template <typename T>
void debug(set<T> &st) {
    for (auto itr = st.begin(); itr != st.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(multiset<T> &ms) {
    for (auto itr = ms.begin(); itr != ms.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(map<T, T> &mp) {
    for (auto itr = mp.begin(); itr != mp.end(); itr++) {
        cerr << itr->first << " " << itr->second << endl;
    }
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << H << " ";
    debug_out(T...);
}

using mint = modint1000000007;

void debug_mint1(vector<mint> &vec) {
    for (int i = 0; i < vec.size(); i++) {
        cerr << vec[i].val() << " ";
    }
    cerr << endl;
}

void debug_mint2(vector<vector<mint>> &vec) {
    for (int i = 0; i < vec.size(); i++) {
        for (int j = 0; j < vec[i].size(); j++) {
            cerr << vec[i][j].val() << " ";
        }
        cerr << endl;
    }
}

void dijkstra(vvpll &graph, ll v, vl &dist) {
    priority_queue<pll, vpll, greater<pll>> pque;
    pque.push(pll(0, v));
    dist[v] = 0;
    while (pque.size()) {
        pll p = pque.top();
        pque.pop();
        if (dist[p.second] != p.first) {
            continue;
        }
        for (auto x : graph[p.second]) {
            if (dist[x.first] > dist[p.second] + x.second) {
                dist[x.first] = dist[p.second] + x.second;
                pque.push(pll(dist[x.first], x.first));
            }
        }
    }
}

const ll INF = 1000000000000000243LL;

int main() {
    ll N, M;
    cin >> N >> M;
    vector<ll> h(M);
    vector<ll> w(M);
    vector<ll> c(M);
    rep(i, M){
        cin >> h[i] >> w[i] >> c[i];
        h[i]--;
        w[i]--;
    }
    vector<ll> dist(2 * N * N, INF);

    vector<vector<ll>> fees(N, vector<ll>(N));
    rep(i, M){
        fees[h[i]][w[i]] = c[i];
    }

    vector<vector<pll>> graph(2 * N * N, vector<pll>(0));

    for (ll i = 0; i < N; i++){
        for (ll j = 0; j < N; j++){
            if (i > 0){
                rep(k, 2){
                    graph[(i - 1) * N + j + k * N * N].push_back(make_pair(i * N + j + k * N * N, 1 + fees[i][j]));
                }
                graph[(i - 1) * N + j].push_back(make_pair(i * N + j + N * N, 1));
            }
            if (j > 0){
                rep(k, 2){
                    graph[i * N + j - 1 + k * N * N].push_back(make_pair(i * N + j + k * N * N, 1 + fees[i][j]));
                }
                graph[i * N + j - 1].push_back(make_pair(i * N + j + N * N, 1));
            }
            if (i < N - 1){
                rep(k, 2){
                    graph[(i + 1) * N + j + k * N * N].push_back(make_pair(i * N + j + k * N * N, 1 + fees[i][j]));
                }
                graph[(i + 1) * N + j].push_back(make_pair(i * N + j + N * N, 1));
            }
            if (j < N - 1){
                rep(k, 2){
                    graph[i * N + j + 1 + k * N * N].push_back(make_pair(i * N + j + k * N * N, 1 + fees[i][j]));
                }
                graph[i * N + j + 1].push_back(make_pair(i * N + j + N * N, 1));
            }
        }
    }

    dijkstra(graph, 0, dist);
    cout << min(dist[N * N - 1], dist[2 * N * N - 1]) << endl;
}