//@formatter:off
#include<bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < int(n); ++i)
#define rrep(i,n) for (int i = int(n)-1; i >= 0; i--)
#define rep2(i,s,n) for (int i = int(s); i < int(n); ++i)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define pb push_back
#define eb emplace_back
#define vi vector<int>
#define vvi vector<vector<int>>
#define vl vector<ll>
#define vvl vector<vector<ll>>
#define vd vector<double>
#define vvd vector<vector<double>>
#define vs vector<string>
#define vc vector<char>
#define vvc vector<vector<char>>
#define vb vector<bool>
#define vvb vector<vector<bool>>
#define vp vector<P>
#define vvp vector<vector<P>>
using namespace std;
using ll = long long;
using P = pair<int,int>;
using LP = pair<ll,ll>;
template<class S,class T> istream& operator>>(istream &is,pair<S,T> &p) { return is >> p.first >> p.second; }
template<class S,class T> ostream& operator<<(ostream &os,const pair<S,T> &p) { return os<<'{'<<p.first<<","<<p.second<<'}'; }
template<class T> istream& operator>>(istream &is,vector<T> &v) { for(T &t:v){is>>t;} return is; }
template<class T> ostream& operator<<(ostream &os,const vector<T> &v) { os<<'[';rep(i,v.size())os<<v[i]<<(i==int(v.size()-1)?"":","); return os<<']'; }
void Yes(bool b) { cout << (b ? "Yes" : "No") << '\n'; }
void YES(bool b) { cout << (b ? "YES" : "NO") << '\n'; }
template<class T> bool chmin(T& a,T b) {if(a > b){a = b; return true;} return false;}
template<class T> bool chmax(T& a,T b) {if(a < b){a = b; return true;} return false;}
const int inf = 1001001001;
const ll linf = 1001001001001001001;
//@formatter:on

struct edge {
    int to;
    ll len;
    
    edge(int to, ll l) : to(to), len(l) {}
};

vl dijkstra(int start, const vector<vector<edge>> &v) {
    int n = v.size();
    vl dist(n, linf);
    priority_queue<pair<ll, int>, vector<pair<ll, int>>, greater<pair<ll, int>>> q;
    q.emplace(0LL, start);
    dist[start] = 0;
    while (!q.empty()) {
        auto p = q.top();
        q.pop();
        if (dist[p.second] < p.first) continue;
        for (auto e : v[p.second]) {
            if (chmin(dist[e.to], p.first + e.len)) {
                q.emplace(p.first + e.len, e.to);
            }
        }
    }
    return dist;
}

using vve = vector<vector<edge>>;

const int dx[4] = {0, 1, 0, -1};
const int dy[4] = {1, 0, -1, 0};

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int n, m;
    cin >> n >> m;
    vvi v(n, vi(n));
    rep(_, m) {
        int h, w, c;
        cin >> h >> w >> c;
        h--;
        w--;
        v[h][w] = c;
    }
    auto toId = [&](int i, int j, int k) {
        return (i * n + j) * 2 + k;
    };
    vve G(n * n * 2);
    rep(i, n) rep(j, n) {
            rep(k, 4) {
                int ni = i + dx[k], nj = j + dy[k];
                if (ni < 0 or ni >= n or nj < 0 or nj >= n) continue;
                G[toId(i, j, 0)].eb(toId(ni, nj, 0), v[ni][nj] + 1);
                G[toId(i, j, 1)].eb(toId(ni, nj, 1), v[ni][nj] + 1);
                G[toId(i, j, 0)].eb(toId(ni, nj, 1), 1);
            }
        }
    cout << dijkstra(toId(0, 0, 0), G)[toId(n - 1, n - 1, 1)] << endl;
}