#include <iostream>
#include <tuple>
#include <cmath>
#include <vector>
#include <algorithm>
using namespace std;
//tuple(t, x, y)
int dist(const tuple<int, int, int>& i, const tuple<int, int, int>& j){
	return ( abs(get<1>(i) - get<1>(j)) + abs(get<2>(i) - get<2>(j)) );
}
int time(const tuple<int, int, int>& i, const tuple<int, int, int>& j){
	return abs( get<0>(i) - get<0>(j) );
}
int main(){
	int n, m;
	cin >> n >> m;
	//n * n, m 个鼹鼠
	vector<tuple<int, int, int>> ham(m);
	vector<int> dp(m, 1);
	for(int i = 0; i < m; i++){
		int t, x, y;
		cin >> t >> x >> y;
		ham[i] = make_tuple(t, x, y);
	} 
	//dp[m] = max (能走到的(t2 - t1 > dist)dp[x] + 1)
	for(int i = 1; i < m; i++){
		for(int j = 0; j < i; j++){
			//如果能走到就更新 
			if(dist(ham[i], ham[j]) <= time(ham[i], ham[j])){
				dp[i] = max(dp[i], dp[j] + 1);
			}
		}
	} 
	cout << *max_element(dp.begin(), dp.end()) << endl;
	return 0;
}