program t3(input,output);
 var
 n,m:integer;
 data:array[1..500]of longint;
 jl:array[1..500]of integer;
  i,j,k,kk,max,q:longint;

 begin
 assign(input,'skill.in');
 assign(output,'skill.out');
 reset(input) ;
 rewrite(output);
 readln(n,m);
 max:=0;    k:=0;
 fillchar(data,sizeof(data),0);
 for i:= 1 to n do
   for j:= 1 to n+1-i do
   begin
   inc(k);
   read(input,data[k]);
   end;
close(input);
for i:= 1 to n do
jl[i]:=1;   kk:=n;
for i:= 2 to n do
 begin
 for j:= 1 to n +1-i do
 begin
 inc(kk);
 data[kk]:=data[kk-n-1+i-1]+data[kk-n-1+i];
 jl[kk]:=jl[kk-n-1+i-1] +jl[kk-n+i-1]+1;
  end;

 if m mod jl[kk] <=(n+1-i ) then
  begin
  max:=0;
   for q:= kk downto kk-(n +1-i) do
   if max< data[q] then max:=data[q];
   max:=max+data[n]*(m-jl[q]);
   writeln(max);
   close(output);
   halt;
  end;
 end;
 end.