#include<bits/stdc++.h>
using namespace std;
#pragma region atcoder
/*#include <atcoder/all>
using namespace atcoder;*/
//using mint = modint998244353;
//using mint = modint1000000007;
#pragma endregion
#pragma region macros
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;
using vs = vector<string>;
using vl = vector<ll>;
using vb = vector<bool>;
using vvi = vector<vector<int>>;
using vvl = vector<vector<ll>>;
#define rep(i, n) for(int i = 0; i < n; i++)
#define REP(i, a, b) for(int i = a; i < b; i++)
#define rrep(i, n) for(int i = n - 1; i >= 0; i--)
#define RREP(i, a, b) for(int i = b - 1; i >= a; i--)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) ((int)(x).size())
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define fi first
#define se second
#pragma endregion
#pragma region debug for var, v, vv
#define debug(var)  do{std::cout << #var << " : ";view(var);}while(0)
template<typename T> void view(T e){std::cout << e << std::endl;}
template<typename T> void view(const std::vector<T>& v){for(const auto& e : v){ std::cout << e << " "; } std::cout << std::endl;}
template<typename T> void view(const std::vector<std::vector<T> >& vv){cout << endl;int cnt = 0;for(const auto& v : vv){cout << cnt << "th : "; view(v); cnt++;} cout << endl;}
#pragma endregion
#pragma region int128
std::ostream &operator<<(std::ostream &dest, __int128_t value) {
  std::ostream::sentry s(dest);
  if (s) {
    __uint128_t tmp = value < 0 ? -value : value;
    char buffer[128];
    char *d = std::end(buffer);
    do {
      --d;
      *d = "0123456789"[tmp % 10];
      tmp /= 10;
    } while (tmp != 0);
    if (value < 0) {
      --d;
      *d = '-';
    }
    int len = std::end(buffer) - d;
    if (dest.rdbuf()->sputn(d, len) != len) {
      dest.setstate(std::ios_base::badbit);
    }
  }
  return dest;
}
#pragma endregion
const ll mod = 1000000007;
const int inf = 1001001001;
const ll INF = 1001001001001001001;

int dx[]={1,0,-1,0};
int dy[]={0,1,0,-1};
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; }
ll rudiv(ll a, ll b) { return a/b+((a^b)>0&&a%b); } //  20 / 3 == 7
ll rddiv(ll a, ll b) { return a/b-((a^b)<0&&a%b); } // -20 / 3 == -7
ll power(ll a, ll p){ll ret = 1; while(p){if(p & 1){ret = ret * a;} a = a * a; p >>= 1;} return ret;}
ll modpow(ll a, ll p){ll ret = 1; while(p){if(p & 1){ret = ret * a % mod;} a = a * a % mod; p >>= 1;} return ret;}

/*--------------------------------------------------------------------------------------------------------------------------------*/
struct var{
    int h, w, u;
    ll cost;
    var(int _h, int _w, ll _cost ,int _u) : h(_h), w(_w), cost(_cost), u(_u){}
    bool operator> (const var &v)const{
        return cost > v.cost;
    }
};
ll dist[502][502][2];
int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    //cout << fixed << setprecision(15);
    int n, m; cin >> n >> m;
    vvl c(n,vl(n));
    rep(i,m){
        int h, w; cin >> h >> w;
        h--, w--;
        ll co; cin >> co;
        c[h][w] = co;
    }
    priority_queue<var, vector<var>, greater<var>> que;
    rep(i,502) rep(j,502) rep(k,2) dist[i][j][k] = INF;
    dist[0][0][0] = dist[0][0][1] = 0;
    que.emplace(0,0,0,0);
    while(que.size()){
        var v = que.top(); que.pop();
        //cout << v.h << " " << v.w << " " << v.cost << " " << v.u << endl;
        rep(k,4){
            int nh = v.h + dx[k], nw = v.w + dy[k];
            if(nh < 0 || nh >= n || nw < 0 || nw >= n) continue;
            if(chmin(dist[nh][nw][v.u], dist[v.h][v.w][v.u] + 1 + c[nh][nw])){
                //cout << nh << " " << nw << " " << dist[nh][nw][u] << " " << u << endl;
                que.emplace(nh, nw, dist[nh][nw][v.u], v.u);
            }
            if(v.u == 0 && chmin(dist[nh][nw][1], dist[v.h][v.w][v.u] + 1)){
                que.emplace(nh, nw, dist[nh][nw][v.u], 1);
            }
        }
    }
    //rep(i,n) rep(j,n) cout << dist[i][j] << " ";
    cout << dist[n - 1][n - 1][1] << endl;
}
/*
   * review you code when you get WA (typo? index?)
   * int overflow, array bounds
   * special cases (n=1?)
*/