program ex(f1,f2);
 type
  zn=array [1..10001,1..1001] of longint;
 var
  a,c:zn; f1,f2:text;
  i,j,k,p,l,m,n,ans:longint;
 begin
  assign(f1,'azshara.in'); reset(f1);
  assign(f2,'azshara.out'); rewrite(f2);
  readln(f1,m,n);
  for i:=1 to n do
   for j:=1 to m do
    read(f1,a[i,j]);
  for i:=1 to m do
   if a[n,i]<>-1 then c[n,i]:=a[n,i];
  for i:=n-1 downto 1 do
   for j:=1 to m do
    if a[i,j]<>-1 then
    begin
     k:=c[i+1,j];
     if (j-1>=1) then if c[i+1,j-1]>k then k:=c[i+1,j-1];
     if (j+1<=m) then if c[i+1,j+1]>k then k:=c[i+1,j+1];
     c[i,j]:=a[i,j]+k;
    end;
  ans:=0;
  for i:=1 to m do if c[1,i]>ans then ans:=c[1,i];
  writeln(f2,ans);
  close(f1);
  close(f2);
 end.