//#include <tourist>
#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
typedef long long ll;
typedef long double ld;
typedef unsigned int uint;
typedef unsigned long long ull;

typedef pair<ll, ll> p;
const int INF = 1e9;
const double eps = 1e-7;
const ll LINF = ll(1e18);
const int MOD = 1000000007;
const int dx[4] = {0, 1, 0, -1}, dy[4] = {-1, 0, 1, 0};
const int Dx[8] = {0, 1, 1, 1, 0, -1, -1, -1}, Dy[8] = {-1, -1, 0, 1, 1, 1, 0, -1};
const long double pi = 4 * atan(1);
#define yes cout << "Yes" << endl
#define YES cout << "YES" << endl
#define no cout << "No" << endl
#define NO cout << "NO" << endl
#define rep(i, n) for (int i = 0; i < n; i++)
#define ALL(v) v.begin(), v.end()
#define debug(v)          \
    cout << #v << ":";    \
    for (auto x : v)      \
    {                     \
        cout << x << ' '; \
    }                     \
    cout << endl;
template <class T>
bool chmax(T &a, const T &b)
{
    if (a < b)
    {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
bool chmin(T &a, const T &b)
{
    if (b < a)
    {
        a = b;
        return 1;
    }
    return 0;
}
//cout<<fixed<<setprecision(15);有効数字15桁
//-std=c++14
//g++ yarudake.cpp -std=c++17 -I .
ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
//ダイクストラ
//LINFにしてあるよ
struct edge
{
    ll to, cost;
};
typedef pair<ll, ll> P;
struct graph
{
    ll V;
    vector<vector<edge>> G;
    vector<ll> d;
    //vector<ll> count;経路の本数
    //vector<ll> prev; // prev[v] := v から復元できる辺たち
    graph(ll n)
    {
        init(n);
    }

    void init(ll n)
    {
        V = n;
        G.resize(V);
        d.resize(V);
        //count.resize(V);
        rep(i, V)
        {
            d[i] = LINF;
            //count[i] = 0;
        }
    }

    void add_edge(ll s, ll t, ll cost)
    {
        edge e;
        e.to = t, e.cost = cost;
        G[s].push_back(e);
    }

    void dijkstra(ll s)
    {
        rep(i, V)
        {
            d[i] = LINF;
            //count[i] = 0;
        }
        d[s] = 0;
        //count[s] = 1;
        priority_queue<P, vector<P>, greater<P>> que;
        que.push(P(0, s));
        while (!que.empty())
        {
            P p = que.top();
            que.pop();
            ll v = p.second;
            if (d[v] < p.first)
                continue;
            for (auto e : G[v])
            {
                if (d[e.to] > d[v] + e.cost)
                {
                    d[e.to] = d[v] + e.cost;
                    que.push(P(d[e.to], e.to));
                    //count[e.to] = count[v];
                    // 復元のための
                    //prev[e.to]=v;
                }
                /*
        else if (d[e.to] == d[v] + e.cost)
                {
                    count[e.to] += count[v];
                    count[e.to] %= MOD;
                }
                */
            }
        }
    }
};
int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    ll n, m;
    cin >> n >> m;
    vector<vector<ll>> c(n, vector<ll>(n, 0));
    rep(i, m)
    {
        ll h, w, C;
        cin >> h >> w >> C;
        h--;
        w--;
        c[h][w] = C;
    }
    graph g(2 * n * n);
    rep(i, n * n)
    {
        int hi = i / n;
        int wi = i % n;
        rep(j, 4)
        {
            int hid = hi + dx[j];
            int wid = wi + dy[j];
            if (hid >= n || hid < 0 || wid >= n || wid < 0)
                continue;
            g.add_edge(hi * n + wi, hid * n + wid, c[hid][wid] + 1);
            g.add_edge(hi * n + wi + n * n, hid * n + wid + n * n, c[hid][wid] + 1);
            if (c[hid][wid])
            {
                g.add_edge(hi * n + wi, hid * n + wid + n * n, 1);
            }
        }
    }
    g.dijkstra(0);
    cout << min(g.d[n * n - 1], g.d[2 * n * n - 1]) << "\n";
}