#include<bits/stdc++.h>
using namespace std;
int m, n; //m，m代表要到达的地点，n代表有几个有颜色的点
int a[110][110]; //1代表黄色，0代表红色，-1代表无色
int ans[110][110];
bool b[110][110];
struct node {
	int x, y, s_color, number;
};
queue<node> q;
int dx[] = {0, -1, 1, 0};
int dy[] = {1, 0, 0, -1};
int bfs(int x, int y) {
	q.push({x, y, a[x][y], 1});
	ans[x][y] = 0;
	b[1][1] = 1;
	while (!q.empty()) {
		node t = q.front();
		q.pop();
		if (t.x == m && t.y == m)
			return ans[m][m];
		for (int i = 0; i < 4; i++) {
			int xx = t.x + dx[i];
			int yy = t.y + dy[i];
			if (xx >= 1 && yy >= 1 && xx <= m && yy <= m && !b[xx][yy]) {
				b[xx][yy] = 1;
				int numb = t.number;
				int an = 0;
				if (a[xx][yy] == -1) {
					if (!numb)
						continue;
					numb = 0;
					a[xx][yy] = a[t.x][t.y];
					an = 2;
				} else if (a[t.x][t.y] != a[xx][yy])
					an = 1, numb = 1;
				else
					numb = 1;
				bool flag = false;
				if (ans[xx][yy] > ans[t.x][t.y] + an) {
					ans[xx][yy] = ans[t.x][t.y] + an;
					flag = true;
				}
				if (flag)
					q.push({xx, yy, a[xx][yy], numb});
			}
		}
	}
	return -1;
}
int main() {
	memset(a, -1, sizeof(a));
	memset(ans, 0x3f, sizeof(ans));
	scanf("%d%d", &m, &n);
	for (int i = 1; i <= n; i++) {
		int x, y, v;
		scanf("%d%d%d", &x, &y, &v);
		a[x][y] = v;
	}
	cout << bfs(1, 1);
	return 0;
}