#define ll long long
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <cstring>
#include <cstdio>
#include <vector>
#include <cmath>
#include <queue>
#include <stack>
#include <list>
#include <map>
#include <set>
using namespace std;
ll n,x,y,t,times[1001][1001],book[1001][1001],ans[1001][1001];
ll head,tail;
struct node{
	ll tx,ty;
}f[10001];
ll next[4][2]={{0,1},{0,-1},{-1,0},{1,0}};
int main(){
	cin>>n;
	memset(times,1e7,sizeof(times));
	for(int i=1;i<=n;i++){
		cin>>x>>y>>t;
		times[x][y]=min(times[x][y],t);
		if(x>0)times[x-1][y]=min(times[x-1][y],t);
		times[x+1][y]=min(times[x+1][y],t);
		if(y>0)times[x][y-1]=min(times[x][y-1],t);
		times[x][y+1]=min(times[x][y+1],t);
	}
	book[0][0]=1;
	for(int head=1;head<=tail;head++){
		if(times[f[head].tx][f[head].ty]==1e7){
			cout<<ans[f[head].tx][f[head].ty];
			return 0;
		}
		for(int i=0;i<4;i++){
			ll dx=f[head].tx+next[i][0];
			ll dy=f[head].ty+next[i][1];
			if(dx>0&&dy>0&&ans[f[head].tx][f[head].ty]+1<times[dx][dy]&&book[dx][dy]==0){
				book[dx][dy]=1;
				ans[dx][dy]=ans[f[head].tx][f[head].ty]+1;
				f[++tail].tx=dx;
				f[tail].ty=dy;
			}
		}
	}
	cout<<-1;
	return 0;
} 

有些是借鉴的题解，但是输出是负一