program s;
var
   i,j,k,w,l:longint;
   f,map:array[0..10000,0..1000] of longint;
   e:text;
begin
   assign(e,'azshara.in');
   reset(e);
   readln(e,w,l);
   for i:=0 to l do
   for j:=0 to w do
   f[i,j]:=0;
   for i:=1 to l do begin
   for j:=1 to w do begin
   read(e,k); map[i,j]:=k;   f[i,j]:=k;
   end;
   readln(e);
   end;
   close(e);

   for i:=1 to l do begin
     for j:=1 to w do  begin
     if map[i,j]=-1 then f[i,j]:=-1 else begin
     k:=f[i-1,j-1];
     if f[i-1,j]>k then k:=f[i-1,j];
     if f[i-1,j+1]>k then k:=f[i-1,j+1];
     f[i,j]:=k+f[i,j];
      end;
     end;
   end;
   k:=f[l,1];
   for i:=2 to w do
   if f[l,i]>k then k:=f[l,i];
   assign(e,'azshara.out');
   rewrite(e);
   writeln(e,k);
   close(e);
end.