#include <cstdio>
inline int abs(int x) { return x >= 0 ? x : -x; }
int t[100010], x[100010], y[100010], f[100010], n, m, ans;
int main()
{
    scanf("%d%d", &n, &m);
    for (int i = 0; i < m; i++) f[i] = 1, scanf("%d%d%d", t + i, x + i, y + i);
    for (int i = 0; i < m; i++)
        for (int j = 0; j < i; j++)
            if (abs(x[i] - x[j]) + abs(y[i] - y[j]) <= abs(t[i] - t[j]) && f[i] < f[j] + 1)
                f[i] = f[j] + 1;
    for (int i = 0; i < m; i++) if (f[i] > ans) ans = f[i];
    printf("%d", ans);
    return 0;
}