var ok:boolean;
    f:text;
    n,op,x,i,max:longint;
begin
assign(f,'operatii.in');
reset(f);
readln(f,n);
ok:=false;
op:=0;
max:=0;
for i:=1 to n do begin
                 read(f,x);
                 if (x<>0) and not ok then begin
                                           ok:=true;
                                           max:=x;
                                           end
                 else
                 if (x<>0) and ok then  begin
                                        if x>max then max:=x;
                                        end
                 else
                     if x=0 then begin
                                 ok:=false;
                                 op:=op+max;
                                 max:=0;
                                 end;
                 end;
close(f);
op:=op+max;
assign(f,'operatii.out');
rewrite(f);
write(f,op);
close(f);
end.