johns_fence

% Enter your code here. Read input from STDIN. Print output to STDOUT
% Your class should be named solution

-module(solution).
-export([main/0]).
read_hights(0, Acc) -> Acc;
read_hights(N, Acc) ->
    {ok, [H]} = io:fread("", "~d"),
    read_hights(N - 1, [H|Acc]).



%smallest(Array, S, L) ->
%    lists:foldl(fun(Idx, {Smallest, SIdx}) ->
%                    E = array:get(Idx, Array),
%                    case E < Smallest of
%                        true -> {E, Idx};
%                        false -> {Smallest, SIdx}
%                    end
%                end, {array:get(S, Array), S} , lists:seq(S, S + L - 1)).

smallest(Array, S, L) -> smallest_1(Array, S, L, {array:get(S, Array), S}).

smallest_1(_, _, 0, {Smallest, SIdx}) -> {Smallest, SIdx};
smallest_1(Array, S, L, {Smallest, SIdx}) ->
    E = array:get(S, Array),
    case E < Smallest of
        true -> smallest_1(Array, S + 1, L -1, {E, S});
        false -> smallest_1(Array, S + 1, L -1, {Smallest, SIdx})
    end.

max_of(A, B, C) ->
    case (A >= B) and (A >= C) of
        true -> A;
        false -> case (B >= A) and (B >= C) of
                     true -> B;
                     false -> case (C >= A) and (C >= B) of
                                  true -> C;
                                  false -> error
                              end
                 end
    end.


max_area(_, _, L, {ResRef, Parent}) when L =< 0 ->
    Parent ! {ResRef, 0};
max_area(Hights, S, L, {ResRef, Parent}) ->
    {Smallest, SIdx} = smallest(Hights, S, L),
    LRef = make_ref(),
    RRef = make_ref(),
    Self = self(),
    spawn(fun() -> max_area(Hights, S, SIdx - S, {LRef, Self}) end),
    spawn(fun() -> max_area(Hights, SIdx + 1, L - SIdx - 1 + S, {RRef, Self}) end),
    TA = Smallest * L,
    LA = receive {LRef, LRes} -> LRes end,
    RA = receive {RRef, RRes} -> RRes end,
    Parent ! {ResRef, max_of(TA, LA, RA)}.



get_area(Hights, S, L) ->
    Ref = make_ref(),
    Self = self(),
    spawn(fun() -> max_area(Hights, S, L, {Ref, Self}) end),
    receive
        {Ref, Res} -> Res
    end.

main() ->
	{ok, [N]} = io:fread("", "~d"),
    Hights = array:from_list(read_hights(N, [])),
    io:format("~w~n", [get_area(Hights, 0, N)]).