#include<bits/stdc++.h>
using namespace std;
#pragma region Macros
#define ll long long
#define ld long double
#define FOR(i,l,r) for(ll i=(l);i<(r);++i)
#define REP(i,n) FOR(i,0,n)
#define REPS(i,n) FOR(i,1,n+1)
#define RFOR(i,l,r) for(ll i=(l);i>=(r);--i)
#define RREP(i,n) RFOR(i,n-1,0)
#define RREPS(i,n) RFOR(i,n,1)
#define pb push_back
#define eb emplace_back
#define SZ(x) ((ll)(x).size())
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
template<class T = ll> using V = vector<T>;
template<class T = ll> using VV = V<V<T>>;
using P = pair<ll, ll>;
#define VEC(type, name, size)\
    V<type> name(size);\
    IN(name)
#define VVEC(type, name, h, w)\
    VV<type> name(h, V<type>(w));\
    IN(name)
#define INT(...)\
    int __VA_ARGS__;\
    IN(__VA_ARGS__)
#define LL(...)\
    ll __VA_ARGS__;\
    IN(__VA_ARGS__)
#define STR(...)\
    string __VA_ARGS__;\
    IN(__VA_ARGS__)
#define CHAR(...)\
    char __VA_ARGS__;\
    IN(__VA_ARGS__)
#define DOUBLE(...)\
    DOUBLE __VA_ARGS__;\
    IN(__VA_ARGS__)
#define LD(...)\
    LD __VA_ARGS__;\
    IN(__VA_ARGS__)
template <class T> void scan(T a) { cin >> a; }
void scan(int &a) { cin >> a; }
void scan(long long &a) { cin >> a; }
void scan(char &a) { cin >> a; }
void scan(double &a) { cin >> a; }
void scan(long double &a) { cin >> a; }
void scan(char a[]) { scanf("%s", a); }
void scan(string &a) { cin >> a; }
template <class T> void scan(V<T> &);
template <class T, class L> void scan(pair<T, L> &);
template <class T> void scan(V<T> &a) { for(auto &i : a) scan(i); }
template <class T, class L> void scan(pair<T, L> &p){ scan(p.first); scan(p.second); }
template <class T> void scan(T &a) { cin >> a; }
void IN() {}
template <class Head, class... Tail> void IN(Head &head, Tail &... tail) { scan(head); IN(tail...); }
template <class T> inline void print(T x){ cout << x << '\n';}
struct inputoutputfaster{
    inputoutputfaster(){
        ios::sync_with_stdio(false);\
        cin.tie(nullptr);
        cout << fixed << setprecision(15);
    }
}inputoutputfaster_;
template <class T> V<T> press(V<T> &x){ 
    V<T> res = x;
    sort(all(res));
    res.erase(unique(all(res)), res.end());
    REP(i, SZ(x)){
        x[i] = lower_bound(all(res), x[i]) - res.begin();
    }
    return res;
}
template<class T> inline bool chmin(T& a, T b) {if (a > b) {a = b; return true; }return false; }
template<class T> inline bool chmax(T& a, T b) {if (a < b) {a = b; return true; }return false; }
inline void Yes(bool b = true) {cout << (b ? "Yes" : "No") << '\n';}
inline void YES(bool b = true) {cout << (b ? "YES" : "NO") << '\n';}
inline void err(bool b = true) {if(b) {cout << -1 << '\n'; exit(0);}}
template<class T> inline void fin(bool b = true, T e = 0) {if(b) {cout << e << '\n'; exit(0);}}
template<class T> T divup(T x, T y) {return (x+(y-1))/y;}
template <typename T> T pow(T a, long long n, T e = 1) {T ret = e; while (n) {if (n & 1) ret *= a; a *= a; n >>= 1; } return ret; }
const ll INF = 1e18;
#pragma endregion
// Graph Template
struct Edge{
    ll to,cost;
    Edge(ll to,ll cost):to(to),cost(cost){}
    bool operator < (const Edge& a) const{
        return cost < a.cost;
    }
};
using Graph = VV<>;
using WGraph = VV<Edge>;

void Read_Graph(Graph &g, int m, bool directed = false){
    REP(i, m){
        LL(u, v); u--; v--;
        g[u].pb(v);
        if(!directed) g[v].pb(u);
    }
}
void Read_Tree(Graph &g, bool directed = false) {Read_Graph(g, SZ(g) - 1, directed);}

void Read_Graph(WGraph &g, int m, bool directed = false){
    REP(i, m){
        LL(u, v, c); u--; v--;
        g[u].pb({v, c});
        if(!directed) g[v].pb({u, c});
    }
}
void Read_Tree(WGraph &g, bool directed = false) {Read_Graph(g, SZ(g) - 1, directed);}

//grid
int n;
int dx[4] = {1,0,-1,0};
int dy[4] = {0,1,0,-1};
int ddx[8] = {1,1,0,-1,-1,-1,0,1,};
int ddy[8] = {0,1,1,1,0,-1,-1,-1};
inline bool inside(int x, int y) {return x >= 0 and x < n and y >= 0 and y < n;}
int gtoi(int x, int y){return x * n + y;}

//s始点のdijkstraを行い、各点のsからの距離を返す
//g:WGraph, s:始点(0-indexed)
V<> dijkstra(WGraph g, int s){
    V<> dist(SZ(g), INF);
    priority_queue<P,vector<P>,greater<P>> que;
    dist[s] = 0;
    que.push(P(0, s));
    while(!que.empty()){
        P p = que.top(); que.pop();
        int v = p.second;
        if(dist[v] < p.first) continue;
        REP(i,SZ(g[v])){
            Edge e = g[v][i];
            if(dist[e.to] > dist[v] + e.cost){
                dist[e.to] = dist[v] + e.cost;
                que.push(P(dist[e.to],e.to));
            }
        }
    }
    return dist;
}

int main(){
    cin >> n;
    INT(m);
    WGraph G(2 * n * n);
    VV<> data(n, V<>(n, 0));
    REP(i, m){
        INT(x, y, c); x--; y--;
        data[x][y] = c;
    }
    REP(i, n) REP(j, n){
        REP(k, 4){
            int nx = i + dx[k], ny = j + dy[k];
            if(inside(nx, ny)){
                G[gtoi(i, j)].pb({gtoi(nx, ny), data[nx][ny] + 1});
                G[gtoi(i, j) + n * n].pb({gtoi(nx, ny) + n * n, data[nx][ny] + 1});
                G[gtoi(i, j)].pb({gtoi(nx, ny) + n * n, 1});
            }
        }
    }
    auto res = dijkstra(G, 0);
    print(min(res[n * n - 1], res[2 * n * n - 1]));
}