#include<iostream>
#include<string>
#include<iomanip>
#include<cmath>
#include<vector>
#include<algorithm>
#include<utility>
#include<queue>

using namespace std;

#define int long long
#define endl "\n"

constexpr long long INF = (long long)1e18;
constexpr long long MOD = 1'000'000'007; 

struct fast_io {
	fast_io(){
		std::cin.tie(nullptr);
		std::ios::sync_with_stdio(false);
	};
} fio;

int N, M;
vector<vector<int>> cost;

struct Node{
    int y, x, z, c;
    
    bool operator > (const Node &n) const {
		return c > n.c;
	}
};

int dx[] = {0, 0, 1, -1};
int dy[] = {1, -1, 0, 0};

int dijkstra(){
    priority_queue<Node, vector<Node>, greater<Node>> Q;
    vector<vector<vector<int>>> d(N, vector<vector<int>>(N, vector<int>(2, INF)));
    
    Q.push({0, 0, 0, 0});
    d[0][0][0] = 0;
    
    while(Q.size()){
        Node cur = Q.top(); Q.pop();
        
        // cout<<cur.y<<" "<<cur.x<<" z = "<<cur.z<<endl;
        // cout<<d[cur.y][cur.x][cur.z]<<" [][] "<<cur.c<<endl;
        if(d[cur.y][cur.x][cur.z] < cur.c) continue;
        
        if(cur.y == N-1 && cur.x == N-1) {
            return cur.c;
        }
        
        // cout<<cur.y<<" "<<cur.x<<endl;
        for(int i = 0; i < 4; i++){
            int y = dy[i] + cur.y, x = dx[i] + cur.x;
            
            if(y < 0 || y >= N || x < 0 || x >= N) continue;
            
            if(cur.z == 0) {
                if(cur.c + 1 < d[y][x][cur.z+1]) {
                    d[y][x][cur.z+1] = cur.c + 1;
                    Q.push({y, x, cur.z + 1, cur.c + 1});
                }
            }
            
            // cout<<"i = "<<i<<endl;
            if(cur.c + 1 + cost[y][x] < d[y][x][cur.z]) {
                d[y][x][cur.z] = cur.c + 1 + cost[y][x];
                // cout<<"<>"<<" y = "<<y<<" x = "<<x<<" "<<d[y][x][cur.z]<<endl;
                Q.push({y, x, cur.z, d[y][x][cur.z]});
            }
        }
    }
    
    return -1;
}

signed main(){
	cout<<fixed<<setprecision(10);
	
	cin>>N>>M;
    
    cost.resize(N, vector<int>(N));

	for(int i = 0; i < M; i++){
        int h, w, c;
        
        cin>>h>>w>>c;
        
        h--, w--;
        
        cost[h][w] = c;
    }
    
    cout<<dijkstra()<<endl;
	
	return 0;
}