Program ferma2;
 var oriz,vt,diag:array [0..1001,0..1001] of int64;
     b1:array [1..1 shl 17] of char;
     i,j,n,min,l,k:longint;
     sum,s:int64;
     fi,fo:text;
begin
assign(fi,'ferma2.in');
 assign(fo,'ferma2.out');
  settextbuf(fi,b1);
   reset(fi); rewrite(fo);
    readln(fi,n,k); l:=n-k; min:=100000000;
 for i:=1 to n do
  for j:=1 to i do begin
                    read(fi,s); sum:=sum+s;
                    oriz[i,j]:=oriz[i,j-1]+s;
                    vt[i,j]:=vt[i-1,j]+oriz[i,j];
                    diag[i,j]:=diag[i-1,j-1]+oriz[i,j];
                    end;
 for i:=1 to n-l+1 do
  for j:=1 to i do begin
   s:=diag[i+l-1,j+l-1]-diag[i-1,j-1]-vt[i+l-1,j-1]+vt[i-1,j-1];
    if s<min then min:=s;
     end;
  write(fo,sum-min);
 close(fo);
end.