program turtle_horse;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
  board, d: array[-2..101, -2..101] of integer;
  w: array[-2..101, -2..101] of boolean;
  n, m, i, j: integer;

function max(x, y: integer): integer;
begin
  if (x > y) then
    result := x
  else
    result := y;
end;

function print(): boolean;
var
  i, j: integer;
begin
  for i := 1 to n do begin
    for j := 1 to m do
      write(d[i, j], ' ');
    writeln;
  end;

  print := true;
end;

begin
  assign(input, 'input.txt');
  reset(input);
  assign(output, 'output.txt');
  rewrite(output);

  read(n, m);

  for i := 1 to n do
    for j := 1 to m do
      read(board[i, j]);

  for i := 1 to n do
    for j := 1 to m do begin
      d[i, j] := 0;
      w[i, j] := false;
    end;

  d[1, 1] := board[1, 1];
  w[1, 1] := true;

  for i := 1 to n do
    for j := 1 to m do
      if ((w[i - 2, j - 1]) and (w[i - 1, j - 2])) then begin
        d[i, j] := d[i, j] + max(d[i - 2, j - 1], d[i - 1, j - 2]) + board[i, j];
        w[i, j] := true;
      end
      else
      if (w[i - 2, j - 1]) then begin
        d[i, j] := d[i, j] + d[i - 2, j - 1] + board[i, j];
        w[i, j] := true;
      end
      else
      if (w[i - 1, j - 2]) then begin
        d[i, j] := d[i, j] + d[i - 1, j - 2] + board[i, j];
        w[i, j] := true;
      end;

  if (d[n, m] > 0) then
    writeln(d[n, m])
  else
    writeln('-1');

  close(input);
  close(output);
end.