BONUS PASCAL

var    a,f:array[0..1005,0..1005] of int64;
       k,n:longint;
    s,max:int64;

procedure nhap;
var i,j:longint;
begin
    readln(n,k);
    for i:=1 to n do
    begin
           for j:=1 to n do read(a[i,j]);
        readln;
    end;
end;

procedure tinh_f;
var i,j:longint;
begin
    for i:=0 to n do f[i,0]:=0;
    for j:=0 to n do f[0,j]:=0;
    for i:=1 to n do
        for j:=1 to n do
              f[i,j]:=f[i-1,j]+f[i,j-1]-f[i-1,j-1]+a[i,j];
end;

function tong(x1,y1,x2,y2:longint):int64;
begin
    exit(F[x2,y2]-f[x1-1,y2]-f[x2,y1-1]+F[x1-1,y1-1]);
end;
procedure giai;
var
   i,j:longint;
begin
    max:=0;
    for x1:=1 to n-k+1 do
           for y1:=1 to n-k+1 do
        begin
            x2:=x1+k-1;
            y2:=y1+k-1;
            s:=tong(x1,y1,x2,y2);
              if > max then max:=s;
        end;
    writeln(max);
end;

begin
    assign(input,'bonus.inp');reset(input);
    assign(output,'bonus.out');rewrite(output);
    nhap;
    tinh_f;
    giai;
    close(input);close(output);
end.