program MayLava;

const
 INF=maxlongint;

var
 map:array[1..10000,0..1001]of longint;
 w,l:longint;

procedure start;
 var
  f:text;
  i,j:longint;
 begin
  fillchar(map,sizeof(map),0);
  assign(f,'azshara.in');
  reset(f);
  readln(f,w,l);
  for i:=1 to l do begin
   for j:=1 to w do
    read(f,map[i,j]);
   readln(f);
  end;
  close(f);
 end;

function max(a,b,c:longint):longint;
 var
  m:longint;
 begin
  m:=0;
  if a>m then m:=a;
  if b>m then m:=b;
  if c>m then m:=c;
  exit(m);
 end;

procedure main;
 var
  i,j:longint;
 begin
  for i:=(l-1) downto 1 do begin
   for j:=1 to w do
    if map[i,j]<>-1 then map[i,j]:=map[i,j]+max(map[i+1,j+1],map[i+1,j],map[i+1,j-1]);
  end;
 end;

procedure print;
 var
  m,i:longint;
  f:text;
 begin
  m:=0;
  for i:=1 to w do
   if map[1,i]>m then m:=map[1,i];
  assign(f,'azshara.out');
  rewrite(f);
  writeln(f,m);
  close(f);
 end;

BEGIN
 start;
 main;
 print;
END.