#include<iostream>  
using namespace std;

int x[10005] = { 0 }, y[10005] = { 0 }, t[10005] = { 0 };
int f[10005] = { 0 };

int main()
{
    int n, m, ans = 0;
    cin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        cin >> t[i] >> x[i] >> y[i];
    }
    for (int i = 1; i <= m; i++)
    {
        for (int j = 1; j <= i; j++)
        {
            int k;
            k = abs(x[i] - x[j]) + abs(y[i] - y[j]);
            if (k <= (t[i] - t[j]))f[i] = max(f[i], f[j] + 1);
        }
        if (f[i] > ans)ans = f[i];
    }
    cout << ans << endl;
    return 0;
}