program skill;
var a,f,c,h,w:array[0..50,0..50]of longint;
    t,k,m,n,i,j,max:longint;
procedure sou(i,j,m,s:longint);
var t,k,x,y:longint;
begin
if i=0 then
  begin
    if s>max then max:=s;
    exit;
  end;
if m>=f[i,j] then
  begin
    for t:=j+2 to (n-t+1) do
      begin
        {for k:=t downto 1 do
          b[i,t+k-i]:=1;}
        sou(i,t,m-f[i,t],s+c[i,t]);
        {for k:=t downto 1 do
          b[i,t+k-i]:=0;}
      end;
  end;
if (m>=h[i,j+1])and(j<=n-i) then
  begin
    t:=j+1;
    sou(i,t,m-h[i,t],s+w[i,t]);
  end;
if m<h[i,j+1]  then
  begin
    x:=i-1;
    y:=j+1;
    sou(x,y,m,s);
  end;
end;

begin
assign(input,'skill.in');
reset(input);
assign(output,'skill.out');
rewrite(output);
readln(n,m);
for t:=1 to n do
  begin
    for k:=1 to n-t+1 do
      read(a[t,k]);
    readln;
  end;
for t:=1 to n do
  begin
    f[1,t]:=1;
    h[1,t]:=1;
    c[1,t]:=a[1,t];
    w[1,t]:=a[1,t];
  end;
for t:=2 to n do
  begin
    for k:=1 to n-t+1 do
    begin
      f[t,k]:=f[t-1,k]+f[t-1,k+1]+1;
      h[t,k]:=h[t-1,k+1]+1;
      c[t,k]:=c[t-1,k]+c[t-1,k+1]+a[t,k];
      w[t,k]:=w[t-1,k+1]+a[t,k];
      if f[t,k]>m then break;
    end;
    if f[t,k]>m then break;
  end;

repeat
  dec(t);
  for i:=1 to n-t+1 do
    begin
      {for j:=t downto 1 do
        b[k,i+k-t]:=1;}
      sou(t,i,m-f[t,i],c[t,i]);
      {for j:=t downto 1 do
        b[k,i+k-t]:=0;}
    end;
until t=1;
writeln(max);
close(output);
end.