Program ferma2;
 var a:array [0..1001,0..1001] of longint;
     b1:array [1..1 shl 15] of char;
     i,j,n,min,s,k,cnt,x,g,h:longint;
     sum:int64;
     fi,fo:text;
{function suma(i,j:longint):longint;
 var x,cnt,s1:longint;
begin
 x:=1; cnt:=1; suma:=0;  s1:=0;
  while cnt<=n-k do begin
                   s1:=s1+a[i,j]-a[i,j-x];
                   inc(x); inc(i); inc(j); inc(cnt);
                   end;
 suma:=s1;
end;}
begin
assign(fi,'ferma2.in');
 assign(fo,'ferma2.out');
settextbuf(fi,b1);
 reset(fi); rewrite(fo);
  readln(fi,n,k);
 for i:=1 to n do begin
  for j:=1 to i do begin read(fi,s); a[i,j]:=a[i,j-1]+s; end;
   sum:=sum+a[i,i];
    readln(fi);
   end;
  min:=100000000;
 for i:=1 to k+1 do
  for j:=1 to i do begin
                   {s:=suma(i,j);}
                   x:=1; cnt:=1; s:=0; g:=i; h:=j;
                    while cnt<=n-k do begin
                                    s:=s+a[g,h]-a[g,h-x];
                                inc(x); inc(g); inc(h); inc(cnt);
                                       end;
                   if s<min then min:=s;
                   end;
 write(fo,sum-min);
 close(fo);
end.