#include<iostream>
#include<cstdio>

using namespace std;

struct node
{
    int x;
    int y;
    int tim;
    long long val;
};
node locate[100000];

bool check(node i1,node i2)
{
    if(abs(i1.x-i2.x)+abs(i1.y-i2.y)<=abs(i1.tim-i2.tim))
        return 1;
    else
        return 0;
}

int main()
{
    int n,m;cin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        cin>>locate[i].tim>>locate[i].x>>locate[i].y;
        locate[i].val=1;
        for(int j=i-1;j>=1;j--)
        {
            if(check(locate[i],locate[j])) locate[i].val=max(locate[i].val,locate[j].val+1);
        }
    }

    cout<<locate[m].val<<endl;
}