program azshara;
var
  a:array[-1..1010,-1..10010]of longint;
  w,l,max:longint;
procedure ini;
var
  i,j:longint;
Begin
  assign(input,'azshara.in');
  assign(output,'azshara.out');
  reset(input); rewrite(output);
  readln(w,l);
  for i:=0 to l+1 do begin
    for j:=0 to w+1  do a[i,j]:=-1;
  end;
  for i:=1 to l do begin
    for j:=1 to w do read(a[i,j]);
    readln;
  end;
End;
procedure go;
var
  i,j,k:longint;
Begin
  for i:=2 to l do begin
    for j:= 1 to w do if a[i,j]<>-1 then begin
      k:=a[i-1,j];
      if a[i-1,j+1]>k then k:=a[i-1,j+1];
      if a[i-1,j-1]>k then k:=a[i-1,j-1];
      a[i,j]:=k+a[i,j];
    end;
  end;
  max:=a[l,1];
  for i:=1 to w do if a[l,i]>max then max:=a[l,i];
End;
Begin
  ini;
  go;
  writeln(max);
  close(input); close(output);
End.