#include <iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<map>
#include<set>
#include<stack>
#include<queue>
#include<math.h>
using namespace std;
typedef long long ll;
#define int long long
#define double long double
typedef vector<int> VI;
typedef pair<int, int> pii;
typedef vector<pii> VP;
typedef vector<string> VS;
typedef priority_queue<int> PQ;
template<class T>bool chmax(T &a, const T &b) { if (a < b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b < a) { a = b; return 1; } return 0; }
#define fore(i,a) for(auto &i:a)
#define REP(i,n) for(int i=0;i<n;i++)
#define eREP(i,n) for(int i=0;i<=n;i++)
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define eFOR(i,a,b) for(int i=(a);i<=(b);++i)
#define SORT(c) sort((c).begin(),(c).end())
#define rSORT(c) sort((c).rbegin(),(c).rend())
#define LB(x,a) lower_bound((x).begin(),(x).end(),(a))
#define UB(x,a) upper_bound((x).begin(),(x).end(),(a))
#define INF 1000000000
#define mod 1000000007
#define eps 1e-12 
//priority_queue<int,vector<int>, greater<int> > q2;

struct edge { int to, cost; };
#define LLINF 922337203685477580

int N, M;
vector<vector<edge> > G;
VI d;
int t[510][510][2];
int co[510][510];

void dikstra(int s) {
	priority_queue<pii, vector<pii>, greater<pii> >que;
	REP(i, N)d[i] = LLINF;
	d[s] = 0;
	que.push(pii(0, s));
	while (!que.empty()) {
		pii p = que.top();
		que.pop();
		int v = p.second;
		if (d[v] < p.first)continue;
		REP(i, G[v].size()) {
			edge e = G[v][i];
			if (d[e.to] > d[v] + e.cost) {
				d[e.to] = d[v] + e.cost;
				que.push(pii(d[e.to], e.to));
			}
		}
	}
}

signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	int pt = 0;
	cin >> N >> M;
	int n = N;
	REP(i, N)REP(j, N) {
		REP(k, 2)t[i][j][k] = pt++;
		co[i][j] = 1;
	}
	N = N * N * 2;
	G.resize(N);
	d.resize(N);
	REP(i, M) {
		int x, y, c; cin >> x >> y >> c;
		x--; y--;
		co[x][y] += c;
	}

	REP(i, n)REP(j, n) {
		int now = t[i][j][0];
		int to;
		if (i + 1 < n) {
			to = t[i + 1][j][0];
			G[now].push_back((edge) { to, co[i + 1][j] });
			if (co[i + 1][j] > 1) {
				to = t[i + 1][j][1];
				G[now].push_back((edge) { to, 1 });
			}
		}
		if (i - 1 >= 0) {
			to = t[i - 1][j][0];
			G[now].push_back((edge) { to, co[i - 1][j] });
			if (co[i - 1][j] > 1) {
				to = t[i - 1][j][1];
				G[now].push_back((edge) { to, 1 });
			}
		}
		if (j + 1 < n) {
			to = t[i][j + 1][0];
			G[now].push_back((edge) { to, co[i][j + 1] });
			if (co[i][j + 1] > 1) {
				to = t[i][j + 1][1];
				G[now].push_back((edge) { to, 1 });
			}
		}
		if (j - 1 >= 0) {
			to = t[i][j - 1][0];
			G[now].push_back((edge) { to, co[i][j - 1] });
			if (co[i][j - 1] > 1) {
				to = t[i][j - 1][1];
				G[now].push_back((edge) { to, 1 });
			}
		}
		now = t[i][j][1];
		if (i + 1 < n) {
			to = t[i + 1][j][1];
			G[now].push_back((edge) { to, co[i + 1][j] });
		}
		if (i - 1 >= 0) {
			to = t[i - 1][j][1];
			G[now].push_back((edge) { to, co[i - 1][j] });
		}
		if (j + 1 < n) {
			to = t[i][j + 1][1];
			G[now].push_back((edge) { to, co[i][j + 1] });
		}
		if (j - 1 >= 0) {
			to = t[i][j - 1][1];
			G[now].push_back((edge) { to, co[i][j - 1] });
		}
	}
	dikstra(t[0][0][0]);
	cout << d[t[n - 1][n - 1][1]] << endl;
	return 0;
}