/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2020.11.06 23:10:25
**/

#include "bits/stdc++.h" 
using namespace std; 
typedef long long ll;




template<typename T>
struct Dijkstra {
private:
    int V;
    struct edge { int to; T cost; };
    vector<vector<edge>> G;
public:
    const T inf = numeric_limits<T>::max();
    
    
    vector<T> d; 
    Dijkstra() {}
    Dijkstra(int V) : V(V) {
        G.resize(V);
    }
    
    Dijkstra<T>& operator=(const Dijkstra<T>& obj) {
        this->V = obj.V;
        this->G = obj.G;
        this->d = obj.d;
        return *this;
    }
    
    
    void add_edge(int from, int to, T weight, bool directed = false) {
        G[from].push_back({to,weight});
        if (!directed) G[to].push_back({from,weight});
    }
    
    
    int add_vertex() {
        G.push_back(vector<edge>());
        return V++;
    }
    void build(int s) {
        d.assign(V, inf); 
        typedef tuple<T, int> P; 
        priority_queue<P, vector<P>, greater<P>> pq;
        d[s] = 0; 
        pq.push(P(d[s], s)); 
        while (!pq.empty()) {
            P p = pq.top(); pq.pop();
            int v = get<1>(p);
            
            if (d[v] < get<0>(p)) continue; 
            for (const edge &e : G[v])
            {
                
                if (d[e.to] > d[v] + e.cost) {
                    d[e.to] = d[v] + e.cost;
                    pq.push(P(d[e.to], e.to));
                }
            }
        }
    }
};
int n;
int id(int h,int w,int used) {
    return h * n + w + n*n*used;
}
int main() {
    int m;cin >> n >> m;
    Dijkstra<ll> g(2*n*n+1);
    int goal = 2*n*n;
    int dx[] = {0,1,0,-1}, dy[] = {1,0,-1,0};
    vector<vector<int>> ryoukin(n,vector<int>(n,0));
    for (int i = 0; i < m; i++) {
        int h,w,c;cin >> h >> w >> c;
        ryoukin[h-1][w-1] = c;
    } 
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            for (int k = 0; k < 4; k++) {
                int x = dx[k] + i, y = dy[k] + j;
                if (x < 0 || x >= n || y < 0 || y >= n) continue;
                if (ryoukin[x][y] > 0) {
                    g.add_edge(id(i,j,0),id(x,y,0),ryoukin[x][y]+1,true);
                    g.add_edge(id(i,j,1),id(x,y,1),ryoukin[x][y]+1,true);
                    g.add_edge(id(i,j,0),id(x,y,1),1,true);
                }
                else {
                    g.add_edge(id(i,j,0),id(x,y,0),1,true);
                    g.add_edge(id(i,j,1),id(x,y,1),1,true);
                }
            }
        }
    }
    g.add_edge(id(n-1,n-1,0),goal,0,true);
    g.add_edge(id(n-1,n-1,1),goal,0,true);
    g.build(id(0,0,0));
    cout << g.d[goal] << endl;
    return 0;
}