program waterfire;
const
fin='azshara.in';
fout='azshara.out';
var
i,j,n,w,maxnum,l:longint;
data,f:array[0..1000,0..10000] of longint;
f1,f2:text;

Function max(a,b:longint):longint;
Begin
if a>b then max:=a else max:=b;
End;

BEGIN
assign(f1,fin);reset(f1);
assign(f2,fout);rewrite(f2);
readln(f1,w,l);
maxnum:=0;fillchar(f,sizeof(f),0);
for i:=1 to l do
 for j:=1 to w do begin
   read(f1,data[i,j]);
   if i=1 then f[i,j]:=data[i,j];
   end;
for i:=2 to l do
  for j:=1 to w do begin
     if (data[i,j]<>-1) then
       begin
          f[i,j]:=max(f[i,j],f[i-1,j]+data[i,j]);
          if (j-1>=1)  then  f[i,j]:=max(f[i,j],f[i-1,j-1]+data[i,j]);
          if (j+1<=w) then  f[i,j]:=max(f[i,j],f[i-1,j+1]+data[i,j]);
          if f[i,j]>maxnum then maxnum:=f[i,j];
        end;
     end;
     writeln(f2,maxnum);
     close(f1);close(f2);
     END.