program azshara;
  const
    max=-1000000;
    maxl=10000;
    maxw=1000;
  type
    sz=array[1..maxl,1..maxw]of longint;
  var
    f1,f2:text;
    a,b:sz;
    l,w:integer;
    ans:longint;
    procedure ini;
      var
        i,j:integer;
      begin
        assign(f1,'azshara.in');reset(f1);
        assign(f2,'azshara.out');rewrite(f2);
        readln(f1,w,l);
        fillchar(a,sizeof(a),0);
        for i:=1 to l do begin
          for j:=1 to w do read(f1,a[i,j]);
          if a[i,j]=-1 then a[i,j]:=max;
        end;
        close(f1);
        for i:=1 to l do
          for j:=1 to w do b[i,j]:=0;
        for i:=1 to w do b[1,i]:=a[1,i];
        ans:=0;
      end;
    procedure main;
      var
        i,j,k:integer;
      begin
        for i:=2 to l do
          for j:=1 to w do
            for k:=-1 to 1 do begin
              if (j+k>0)and(j+k<=w) then
              if b[i-1,j+k]+a[i,j]>b[i,j] then b[i,j]:=b[i-1,j+k]+a[i,j];
            end;
        for i:=1 to w do if b[l,i]>ans then ans:=b[l,i];
      end;
  begin
    ini;
    main;
    writeln(f2,ans);
    close(f2);
  end.