RT。

代码：

var
n,m,i,j,x,y,z,max:longint;
s:Array[-3..5005,-3..5005]of longint;
 begin
  readln(n,m);
  for i:=1 to n do
   begin
    readln(x,y,z);
    s[x,y]:=z;
   end;
  for i:=1 to 5001 do
   for j:=1 to 5001 do
    s[i,j]:=s[i,j-1]+s[i-1,j]-s[i-1,j-1]+s[i,j];
  if m>=n then begin writeln(s[n,n]);halt; end;
  for i:=0 to 5001-m do
   for j:=0 to 5001-m do
    if s[i+m-1,j+m-1]-s[i-1,j+m-1]-s[i+m-1,j-1]+s[i-1,j-1]>max then
     max:=s[i+m-1,j+m-1]-s[i-1,j+m-1]-s[i+m-1,j-1]+s[i-1,j-1];

  writeln(max);
 end.

详情：