#include <bits/stdc++.h>
using namespace std;
using lint = long long;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(nullptr), ios::sync_with_stdio(false), cout << fixed << setprecision(20); }; } fast_ios_;
#define ALL(x) (x).begin(), (x).end()
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template <typename T, typename V>
void ndarray(vector<T>& vec, const V& val, int len) { vec.assign(len, val); }
template <typename T, typename V, typename... Args> void ndarray(vector<T>& vec, const V& val, int len, Args... args) { vec.resize(len), for_each(begin(vec), end(vec), [&](T& v) { ndarray(v, val, args...); }); }
template <typename T> bool chmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; }
template <typename T> bool chmin(T &m, const T q) { if (m > q) {m = q; return true;} else return false; }
template <typename T1, typename T2> pair<T1, T2> operator+(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first + r.first, l.second + r.second); }
template <typename T1, typename T2> pair<T1, T2> operator-(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first - r.first, l.second - r.second); }
template <typename T> vector<T> srtunq(vector<T> vec) { sort(vec.begin(), vec.end()), vec.erase(unique(vec.begin(), vec.end()), vec.end()); return vec; }
template <typename T> istream &operator>>(istream &is, vector<T> &vec) { for (auto &v : vec) is >> v; return is; }
template <typename T> ostream &operator<<(ostream &os, const vector<T> &vec) { os << '['; for (auto v : vec) os << v << ','; os << ']'; return os; }
#if __cplusplus >= 201703L
template <typename... T> istream &operator>>(istream &is, tuple<T...> &tpl) { std::apply([&is](auto &&... args) { ((is >> args), ...);}, tpl); return is; }
template <typename... T> ostream &operator<<(ostream &os, const tuple<T...> &tpl) { std::apply([&os](auto &&... args) { ((os << args << ','), ...);}, tpl); return os; }
#endif
template <typename T> ostream &operator<<(ostream &os, const deque<T> &vec) { os << "deq["; for (auto v : vec) os << v << ','; os << ']'; return os; }
template <typename T> ostream &operator<<(ostream &os, const set<T> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <typename T, typename TH> ostream &operator<<(ostream &os, const unordered_set<T, TH> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <typename T> ostream &operator<<(ostream &os, const multiset<T> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <typename T> ostream &operator<<(ostream &os, const unordered_multiset<T> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &pa) { os << '(' << pa.first << ',' << pa.second << ')'; return os; }
template <typename TK, typename TV> ostream &operator<<(ostream &os, const map<TK, TV> &mp) { os << '{'; for (auto v : mp) os << v.first << "=>" << v.second << ','; os << '}'; return os; }
template <typename TK, typename TV, typename TH> ostream &operator<<(ostream &os, const unordered_map<TK, TV, TH> &mp) { os << '{'; for (auto v : mp) os << v.first << "=>" << v.second << ','; os << '}'; return os; }
#ifdef HITONANODE_LOCAL
#define dbg(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ") " << __FILE__ << endl
#else
#define dbg(x) {}
#endif

template<typename T>
struct ShortestPath
{
    int V, E;
    int INVALID = -1;
    std::vector<std::vector<std::pair<int, T>>> to;
    ShortestPath() = default;
    ShortestPath(int V) : V(V), E(0), to(V) {}
    void add_edge(int s, int t, T len) {
        assert(0 <= s and s < V);
        assert(0 <= t and t < V);
        to[s].emplace_back(t, len);
        E++;
    }

    std::vector<T> dist;
    std::vector<int> prev;
    // Dijkstra algorithm
    // Complexity: O(E log E)
    void Dijkstra(int s) {
        assert(0 <= s and s < V);
        dist.assign(V, std::numeric_limits<T>::max());
        dist[s] = 0;
        prev.assign(V, INVALID);
        using P = std::pair<T, int>;
        std::priority_queue<P, std::vector<P>, std::greater<P>> pq;
        pq.emplace(0, s);
        while(!pq.empty()) {
            T d;
            int v;
            std::tie(d, v) = pq.top();
            pq.pop();
            if (dist[v] < d) continue;
            for (auto nx : to[v]) {
                T dnx = d + nx.second;
                if (dist[nx.first] > dnx) {
                    dist[nx.first] = dnx, prev[nx.first] = v;
                    pq.emplace(dnx, nx.first);
                }
            }
        }
    }

    // Bellman-Ford algorithm
    // Complexity: O(VE)
    bool BellmanFord(int s, int nb_loop) {
        assert(0 <= s and s < V);
        dist.assign(V, std::numeric_limits<T>::max());
        dist[s] = 0;
        prev.assign(V, INVALID);
        for (int l = 0; l < nb_loop; l++) {
            bool upd = false;
            for (int v = 0; v < V; v++) {
                if (dist[v] == std::numeric_limits<T>::max()) continue;
                for (auto nx : to[v]) {
                    T dnx = dist[v] + nx.second;
                    if (dist[nx.first] > dnx) {
                        dist[nx.first] = dnx, prev[nx.first] = v;
                        upd = true;
                    }
                }
            }
            if (!upd) return true;
        }
        return false;
    }
    // Warshall-Floyd algorithm
    // Complexity: O(E + V^3)
    std::vector<std::vector<T>> dist2d;
    void WarshallFloyd() {
        dist2d.assign(V, std::vector<T>(V, std::numeric_limits<T>::max()));
        for (int i = 0; i < V; i++) {
            dist2d[i][i] = 0;
            for (auto p : to[i]) dist2d[i][p.first] = min(dist2d[i][p.first], p.second);
        }
        for (int k = 0; k < V; k++) {
            for (int i = 0; i < V; i++) {
                if (dist2d[i][k] = std::numeric_limits<T>::max()) continue;
                for (int j = 0; j < V; j++) {
                    if (dist2d[k][j] = std::numeric_limits<T>::max()) continue;
                    dist2d[i][j] = min(dist2d[i][j], dist2d[i][k] + dist2d[k][j]);
                }
            }
        }
    }
};

int main()
{
    int N, M;
    cin >> N >> M;
    ShortestPath<lint> graph(N * N * 2);
    vector cost(N, vector<lint>(N));
    while (M--) {
        int h, w;
        int c;
        cin >> h >> w >> c;
        h--, w--;
        cost[h][w] += c;
    }
    REP(i, N) REP(j, N) cost[i][j]++;
    const int D = N * N;
    array<int, 4> dx { 1, -1, 0, 0 };
    array<int, 4> dy { 0, 0, 1, -1 };
    REP(i, N)
    REP(j, N)
    {
        REP(d, 4) {
            int ni = i + dx[d], nj = j + dy[d];
            if (ni < 0 or nj < 0 or ni >= N or nj >= N) {
                continue;
            }
            graph.add_edge(i * N + j, ni * N + nj, cost[ni][nj]);
            graph.add_edge(D + i * N + j, D + ni * N + nj, cost[ni][nj]);
            graph.add_edge(i * N + j, D + ni * N + nj, 1);
        }
    }
    graph.Dijkstra(0);
    dbg(graph.dist);
    cout << graph.dist.back() << '\n';
}