#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i = 0; i < n; i++)
#define rep2(i, x, n) for(int i = x; i <= n; i++)
#define rep3(i, x, n) for(int i = x; i >= n; i--)
#define each(e, v) for(auto &e: v)
#define pb push_back
#define eb emplace_back
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define sz(x) (int)x.size()
using ll = long long;
using pii = pair<int, int>;
using pil = pair<int, ll>;
using pli = pair<ll, int>;
using pll = pair<ll, ll>;
#define pq(type, name) priority_queue<type> name
#define iq(type, name) priority_queue<type, vector<type>, greater<type>> name
const int inf = (1<<30)-1;
const ll INF = (1LL<<60)-1;
const double pi = acos(-1.0);
const double EPS = 1e-10;
template<typename T> bool chmax(T &x, const T &y){
    if(x < y) {x = y; return true;}
    return false;
}
template<typename T> bool chmin(T &x, const T &y){
    if(x > y) {x = y; return true;}
    return false;
}
void in() {}
template<typename Head, typename ...Tail> void in(Head &&head, Tail &&...tail){
    cin >> head;
    in(forward<Tail>(tail)...);
}
void out() {cout << '\n';}
template<typename Head, typename ...Tail> void out(Head &&head, Tail &&...tail){
    cout << head << ' ';
    out(forward<Tail>(tail)...);
}
void outn() {}
template<typename Head, typename ...Tail> void outn(Head &&head, Tail &&...tail){
    cout << head << '\n';
    outn(forward<Tail>(tail)...);
}
template<typename T, typename U> void in(pair<T, U> &p){
    cin >> p.first >> p.second;
}
template<typename T, typename U> void out(pair<T, U> p){
    cout << p.first << ' ' << p.second << '\n';
}
using vi = vector<int>;
using vll = vector<ll>;
#define vec1(type, name, ...) vector<type> name(__VA_ARGS__)
#define VEC1(type, ...) vector<type>(__VA_ARGS__)
#define vec2(type, name, a, ...) vector<vector<type>> name(a, VEC1(type, __VA_ARGS__))
#define VEC2(type, a, ...) vector<vector<type>>(a, VEC1(type, __VA_ARGS__))
#define vec3(type, name, a, b, ...) vector<vector<vector<type>>> name(a, VEC2(type, b, __VA_ARGS__))
#define VEC3(type, a, b, ...) vector<vector<vector<type>>>(a, VEC2(type, b, __VA_ARGS__))
#define vec4(type, name, a, b, c, ...) vector<vector<vector<vector<type>>>> name(a, VEC3(type, b, c, __VA_ARGS__))
#define VEC4(type, a, b, c, ...) vector<vector<vector<vector<type>>>>(a, VEC3(type, b, c, __VA_ARGS__))
#define vec5(type, name, a, b, c, d, ...) vector<vector<vector<vector<vector<type>>>>> name(a, VEC4(type, b, c, d, __VA_ARGS__))
#define VEC5(type, a, b, c, d, ...) vector<vector<vector<vector<vector<type>>>>>(a, VEC4(type, b, c, d, __VA_ARGS__))
template<typename T> void vin(vector<T> &a){
    rep(i, sz(a)) cin >> a[i];
}
template<typename T> void vout(const vector<T> &a){
    for(auto &e: a) cout << e << ' ';
    cout << '\n';
}
template<typename T> void voutn(const vector<T> &a){
    for(auto &e: a) cout << e << '\n';
}
template<typename T> void unique(vector<T> &a){
    sort(all(a)), a.erase(unique(all(a)), a.end());
}
vector<int> iota(int n){
    vector<int> ret(n);
    iota(all(ret), 0);
    return ret;
}
template<typename T> vector<int> iota(const vector<T> &a, bool greater = false){
    vector<int> ret = iota(sz(a));
    sort(all(ret), [&](int i, int j){
        return (a[i] < a[j])^greater;
    });
    return ret;
}
struct io_setup{
    io_setup(){
        ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        cout << fixed << setprecision(15);
    }
} io_setup;
#define VEC(type, name, n) vector<type> name(n); vin(name)
#define INT(...) int __VA_ARGS__; in(__VA_ARGS__)
#define LL(...) ll __VA_ARGS__; in(__VA_ARGS__)
#define CHAR(...) char __VA_ARGS__; in(__VA_ARGS__)
#define STR(...) string __VA_ARGS__; in(__VA_ARGS__)
#define DBL(...) double __VA_ARGS__; in(__VA_ARGS__)
const int MOD = 1000000007;
//const int MOD = 998244353;

template<typename T>
struct Weighted_Graph{
    struct edge{
        int to; T cost;
        edge(int to, T cost) : to(to), cost(cost) {}
    };

    vector<vector<edge>> es;
    vector<T> d;
    const T INF_T;
    const int n;

    Weighted_Graph(int n) : INF_T(numeric_limits<T>::max()), n(n){
        es.resize(n), d.resize(n);
    }

    void add_edge(int from, int to, T cost, bool directed = false){
        es[from].eb(to, cost);
        if(!directed) es[to].eb(from, cost);
    }

    T dijkstra(int s, int t){
        fill(all(d), INF_T);
        using P = pair<T, int>;
        priority_queue<P, vector<P>, greater<P> > que;
        que.emplace(d[s] = 0, s);
        while(!que.empty()){
            auto [p, i] = que.top(); que.pop();
            if(p > d[i]) continue;
            for(auto &e: es[i]){
                if(chmin(d[e.to], d[i]+e.cost)) que.emplace(d[e.to], e.to);
            }
        }
        return d[t];
    }
};

int main(){
    INT(N, M);
    vec2(ll, c, N, N, 0);
    rep(i, M){
        int x, y; cin >> x >> y; x--, y--;
        cin >> c[x][y];
    }
    Weighted_Graph<ll> G(2*N*N);
    int dx[] = {1, 0, -1, 0}, dy[] = {0, 1, 0, -1};
    rep(i, N){
        rep(j, N){
            rep(k, 4){
                int ni = i+dx[k], nj = j+dy[k];
                if(ni < 0 || N <= ni || nj < 0 || N <= nj) continue;
                int s = N*i+j, t = N*ni+nj;
                ll w = 1+c[ni][nj];
                G.add_edge(s, t, w, true), G.add_edge(N*N+s, N*N+t, w, true), G.add_edge(s, N*N+t, 1, true);
            }
        }
    }
    out(G.dijkstra(0, 2*N*N-1));
}