var n,k,i,nr1,nr2,max:longint;
    f:text;

begin
  assign(f,'operatii.in');
  reset(f);
  readln(f,n);
  i:=1; k:=0; max:=0;
  while (i<=n) do
    begin
      read(f,nr1);
      while (nr1=0) and (i<=n) do begin read(f,nr1); inc(i); end;
      nr2:=nr1;
      read(f,nr1);
      while (nr1>=nr2) and (i<=n) do
        begin
          if nr1>max then max:=nr1;
          nr2:=nr1;
          read(f,nr1);
        end;
      inc(k,nr2);
      while (nr1<=nr2) and (i<=n) do
        begin
          nr2:=nr1;
          read(f,nr1);
          inc(i);
        end;
  end;
  close(f);
  assign(f,'operatii.out');
  rewrite(f);
  write(f,k);
  close(f);
end.