-module(missing_integer).
-export([missing_integer/1]).

missing_integer(A) ->
    Positives = [V || V <- lists:usort(A), V > 0],
    find_missing(Positives, 1).

find_missing([], Min) ->
    Min;
find_missing([V | Rest], Min) ->
    case V =:= Min of
        true -> find_missing(Rest, Min + 1);
        false -> Min
    end.