#include <cstdio>

#include <iostream>

#define N 1001

#define M 10001

#define abs(x) ((x) < 0 ? -(x) : (x))

#define max(x, y) ((x) > (y) ? (x) : (y))

int n, m, ans;

int s[M][3], f[N], mx[N];

inline int read()

{

	int x = 0, f = 1;

	char ch = getchar();

	for(; !isdigit(ch); ch = getchar()) if(ch == '-') f = -1;

	for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - '0';

	return x * f;

}

int main()

{

	int i, j, k, x, y, z;

	n = read();

	m = read();

	for(k = 1; k <= m; k++)

	{

		s[k][0] = read();

		s[k][1] = read();

		s[k][2] = read();

		f[k] = 1;

		for(i = k - 1; i >= 1; i--)

		{

			if(f[k] >= mx[i] + 1) break;

			if(s[k][0] - s[i][0] >= abs(s[k][1] - s[i][1]) + abs(s[k][2] - s[i][2]))

				f[k] = max(f[k], f[i] + 1);

		}

		ans = max(ans, f[k]);

		mx[k] = max(mx[k - 1], f[k]);

	}

	printf("%d\n", ans);

	return 0;

}