program cch(input,output);
var
 i,j,l,w,ans:longint;
 data:array[1..1000] of longint;
 f,g:array[1..1000] of longint;
begin
 assign(input,'azshara.in');
 assign(output,'azshara.out');
 reset(input);
 rewrite(output);
 readln(w,l);
 for i:=1 to w do read(data[i]);
 for i:=1 to w do
  f[i]:=data[i];
 for i:=2 to l do
  begin
   for j:=1 to w do g[j]:=f[j];
   for j:=1 to w do read(data[j]);
   for j:=1 to w do
    if data[j]<>-1 then
     begin
      f[j]:=0;
      if (g[j]<>-1)and(g[j]>f[j]) then f[j]:=g[j];
      if (j-1>=1)and(g[j-1]<>-1)and(g[j-1]>f[j]) then
       f[j]:=g[j-1];
      if (j+1<=w)and(g[j+1]<>-1)and(g[j+1]>f[j]) then
       f[j]:=g[j+1];
      inc(f[j],data[j]);
    end
   else f[j]:=-1;
  end;
 ans:=0;
 for i:=1 to w do
  if ans<f[i] then ans:=f[i];
 write(ans);
 close(input);
 close(output);
end.