#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
const int nmax=1086;
const int mmax=10086;


int n,m;
int ans=0;
int f[mmax];


class moles
{
public:
	int x,y;
	int time;
}moles[mmax];



void PreDo()
{
	scanf("%d%d",&n,&m);
	for(int i=1;i<=m;i++)
	{
		scanf("%d%d%d",&moles[i].time,&moles[i].x,&moles[i].y);
		f[i]=1;
	}
}


int main()
{
	freopen("mouse.in","r",stdin);
	freopen("mouse.out","w",stdout);
	PreDo();
	for(int i=1;i<=m;i++)
	{
		for(int j=1;j<=i-1;j++)
		{
			if(f[i]<f[j]+1)
			{
				if((abs(moles[i].x-moles[j].x)+abs(moles[i].y-moles[j].y))<=moles[i].time-moles[j].time)
				{
					f[i]=f[j]+1;
				}
			}
		}
	}
	for(int i=1;i<=m;i++)
	{
		if(f[i]>ans)
		{
			ans=f[i];
		}
	}
	printf("%d\n",ans);
	return 0;
}