program azshara;
type
fxz1=array[1..10000,0..1001] of longint;
var
f1,f2:text;
map,ans:fxz1;
n,m,j,i,max,k:longint;
begin
assign(f1,'azshara.in');
assign(f2,'azshara.out');
reset(f1);rewrite(f2);
readln(f1,m,n);
for i:=1 to n do
begin
for j:=1 to m do
read(f1,map[i,j]);
readln(f1);
end;

{................................}
for i:=1 to m do
ans[1,i]:=map[1,i];
for i:=2 to n do
begin
for j:=1 to m do
if map[i,j]<>-1 then begin max:=0;
                           for k:=-1 to 1 do
                           if ans[i-1,j+k]>=max then max:=ans[i-1,j+k];
                           ans[i,j]:=map[i,j]+max;
                     end;
end;
max:=0;
for i:=1 to m do
if ans[n,i]>=max then max:=ans[n,i];
if max<0 then max:=0;
writeln(f2,max);
close(f1);close(f2);
end.