#include "bits/stdc++.h"
using namespace std;
using ll = long long;
using P = pair<ll, pair<ll, ll>>;
ll INF = (1LL << 60);
int v, e;
vector<pair<ll, ll>>edge[1000010];


vector<vector<ll>> dijkstra(int s) {
	priority_queue<P, vector<P>, greater<P>>pq;
	vector<vector<ll>>dist(v, vector<ll>(2, INF));
	dist[s][0] = 0;
	pq.push({ dist[s][0],{s, 0} });
	while (!pq.empty()) {
		P p = pq.top(); pq.pop();
		ll d = p.first, from = p.second.first;
		ll tmp = p.second.second;
		if (dist[from][tmp] < d)continue;
		for (auto nv : edge[from]) {
			int to = nv.first; ll cost = nv.second;
			if (dist[from][tmp] + cost < dist[to][tmp]) {
				dist[to][tmp] = dist[from][tmp] + cost;
				pq.push({ dist[to][tmp],{to, tmp} });
			}
			if (tmp == 0 && cost > 1) {
				if (dist[from][tmp] + 1 < dist[to][1]) {
					dist[to][1] = dist[from][tmp] + 1;
					pq.push({ dist[to][1],{to, 1} });
				}
			}
		}
	}
	return dist;
}
ll cost[510][510];
int main() {
	cin >> v >> e; 
	for (int i = 0; i < 510; i++) {
		for (int j = 0; j < 510; j++) {
			cost[i][j] = 1;
		}
	}
	for (int i = 0; i < e; i++) {
		ll h, w, c; cin >> h >> w >> c;
		cost[h - 1][w - 1] += c;
	}
	for (int i = 0; i < v; i++) {
		for (int j = 0; j < v; j++) {
			if (i + 1 < v) {
				edge[i*v + j].push_back({ (i + 1)*v + j, cost[i + 1][j] });
				edge[(i + 1)*v + j].push_back({ i*v + j, cost[i][j] });
			}
			if (j + 1 < v) {
				edge[i*v + j].push_back({ i*v + j + 1, cost[i][j + 1] });
				edge[i*v + (j + 1)].push_back({ i*v + j, cost[i][j] });
			}
		}
	}
	v *= v;
	vector<vector<ll>>dist = dijkstra(0);
	cout << min(dist[v - 1][0], dist[v - 1][1]) << endl;

}