program bly(input,output);
type
  t1=array[0..10000,0..10000] of longint;
var
  map:t1;
  f:array[1..3,1..2] of integer;
  w,l,max:longint;
  i,j:integer;
  f1,f2:text;

  procedure dg(hang,lie,money:integer);
  var
    i0,x,y:integer;
  begin
    if hang=l+1 then begin
      if money>max then max:=money;
    end
    else begin
      money:=money+map[hang,lie];
      for i0:=1 to 3 do begin
        x:=hang+1;
        y:=lie+f[i0,2];
        if (map[x,y]<>-1)and(x<=l+2)and(y<=w)and(y>0) then
          dg(x,y,money);
      end;
    end;
  end;
begin
  f[1,1]:=1; f[1,2]:=-1;
  f[2,1]:=1; f[2,2]:=0;
  f[3,1]:=1; f[3,2]:=1;
  assign(f1,'azshara.in');
  reset(f1);
  readln(f1,w,l);
  for i:=1 to l do begin
    for j:=1 to w do begin
      read(f1,map[i,j]);
    end;
    readln(f1);
  end;
  assign(f2,'azshara.out');
  rewrite(f2);
  dg(0,0,0);
  writeln(f2,max);
  close(f2);
end.