//*
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
//*/

#include <bits/stdc++.h>

// #include <atcoder/all>

using namespace std;
// using namespace atcoder;

#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl;
#define DEBUG_MAT(v) cerr<<#v<<endl;for(int i=0;i<v.size();i++){for(int j=0;j<v[i].size();j++) {cerr<<v[i][j]<<" ";}cerr<<endl;}
typedef long long ll;
// #define int ll
 
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define rep1(i,n) for(int i=1;i<=(int)(n);i++)
#define rrep(i,n) for(int i=(int)(n)-1;i>=0;i--)
#define rrep1(i,n) for(int i=(int)(n);i>0;i--)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),c.end()
void YES(bool t=true) {cout<<(t?"YES":"NO")<<endl;}
void Yes(bool t=true) {cout<<(t?"Yes":"No")<<endl;}
void yes(bool t=true) {cout<<(t?"yes":"no")<<endl;}
void NO(bool t=true) {cout<<(t?"NO":"YES")<<endl;}
void No(bool t=true) {cout<<(t?"No":"Yes")<<endl;}
void no(bool t=true) {cout<<(t?"no":"yes")<<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 (a>b) { a = b; return 1; } return 0; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = (ll)1e18 + 1;
const long double pi = 3.1415926535897932384626433832795028841971L;
#define Sp(p) cout<<setprecision(25)<< fixed<<p<<endl;
// int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
// int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
vi dx = {-1, 0, 1, 0}, dy = {0, -1, 0, 1};
// vi dx2 = { 1,1,0,-1,-1,-1,0,1 }, dy2 = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);
const ll MOD = 1000000007;
// const ll MOD = 998244353;
// #define mp make_pair
//#define endl '\n'



signed main() {
    fio();
    
    int n, m;
    cin >> n >> m;
    vector<vll> dist(n, vll(n, vl(2, INF)));
    dist[0][0][0] = 0;
    vll c(n, vl(n));
    rep (i, m) {
        int y, x, cc;
        cin >> y >> x >> cc;
        y--; x--;
        c[y][x] = cc;
    }

    using P = pair<pll, pii>;
    priority_queue<P, vector<P>, greater<P>> pq;
    pq.push(P(pll(0, 0), pii(0, 0)));
    while (pq.size()) {
        P temp = pq.top();
        pq.pop();
        ll cost = temp.first.first, k = temp.first.second, y = temp.second.first, x = temp.second.second;
        if (cost > dist[y][x][k]) continue;

        rep (i, 4) {
            int ny = y + dy[i], nx = x + dx[i];
            if (not in(ny, 0, n) or not in(nx, 0, n)) continue;
            rep (j, 2) {
                int nk = k + j;
                if (nk == 2) break;
                ll ncost;
                if (j == 0) ncost = cost + 1 + c[ny][nx];
                else ncost = cost + 1;
                if (dist[ny][nx][nk] > ncost) {
                    dist[ny][nx][nk] = ncost;
                    pq.push(P(pll(ncost, nk), pii(ny, nx)));
                }
            }
        }
    }
    cout << dist[n - 1][n - 1][1] << endl;
}