#include<iostream>
using namespace std;
int r[150][150];
int a,b,x,y,c,ans=314159265;
void dfs(int x,int y,int money,bool magic){
	int t=r[x][y];
	if(r[x][y]==-1)return;
	if(!x)return;
	if(!y)return;
	if(x>a)return;
	if(y>a)return;
	r[x][y]=-1;
	if(x==a&&y==a){
		ans=min(ans,money);
		return;
	}
	if(!magic){
		if(r[x][y]==r[x][y+1]){
			dfs(x,y+1,money,0);
		}else if(r[x][y+1]){
			dfs(x,y+1,money+1,0);
		}else{
			int col=r[x][y+1];
			dfs(x,y+1,money+2,1);
			r[x][y+1]=col;
		}
		if(r[x][y]==r[x+1][y]){
			dfs(x+1,y,money,0);
		}else if(r[x+1][y]){
			dfs(x+1,y,money+1,0);
		}else{
			int col=r[x+1][y];
			dfs(x+1,y,money+2,1);
			r[x+1][y]=col;
		}
		if(r[x][y]==r[x][y-1]){
			dfs(x,y-1,money,0);
		}else if(r[x][y-1]){
			dfs(x,y-1,money+1,0);
		}else{
			int col=r[x][y-1];
			dfs(x,y-1,money+2,1);
			r[x][y-1]=col;
		}
		if(r[x][y]==r[x-1][y]){
			dfs(x-1,y,money,0);
		}else if(r[x-1][y]){
			dfs(x-1,y,money+1,0);
		}else{
			int col=r[x-1][y];
			dfs(x-1,y,money+2,1);
			r[x-1][y]=col;
		}
	}else{
		if(r[x][y]==r[x][y+1]){
			dfs(x,y+1,money,0);
		}else if(r[x][y+1]){
			dfs(x,y+1,money+1,0);
		}else{
			return;
		}
		if(r[x][y]==r[x+1][y]){
			dfs(x+1,y,money,0);
		}else if(r[x+1][y]){
			dfs(x+1,y,money+1,0);
		}else{
			return;
		}
		if(r[x][y]==r[x][y-1]){
			dfs(x,y-1,money,0);
		}else if(r[x][y-1]){
			dfs(x,y-1,money+1,0);
		}else{
			return;
		}
		if(r[x][y]==r[x-1][y]){
			dfs(x-1,y,money,0);
		}else if(r[x-1][y]){
			dfs(x-1,y,money+1,0);
		}else{
			return;
		}
	}
	r[x][y]=t;
}
int main(){
	cin>>a>>b;
	for(int i=0;i<b;i++){
		cin>>x>>y>>c;
		if(c==0)c=2;
		r[x][y]=c;
	}
	dfs(1,1,0,0);
	if(ans==314159265)ans=-1;
	cout<<ans;
	return 0;
}