1 var i,j,n,m,ans:longint;
 2     f,time,x,y:array[0..15000] of longint;
 3 function max(x,y:longint):longint;
 4  begin
 5  if x>y then exit(x) else exit(y);
 6  end;
 7 procedure main;
 8  begin
 9  readln(n,m);ans:=0;
10  for i:=1 to m do
11   begin
12   f[i]:=1;
13   readln(time[i],x[i],y[i]);
14   for j:=i-1 downto 1 do
15    if time[i]-time[j]>=abs(x[i]-x[j])+abs(y[i]-y[j])
16    then f[i]:=max(f[i],f[j]+1);
17   ans:=max(ans,f[i]);
18   end;
19  writeln(ans);
20  end;
21 begin
22  main;
23 end.