N = int(input())
W = list(map(int, input().split()))

MEMO = {}


def check_memo_and_jduge(matrix, W):
    global MEMO

    true_list = list()
    false_list = list()
    for i, x in enumerate(matrix):
        if x:
            true_list.append(W[i])
        else:
            false_list.append(W[i])

    true_list_str = ",".join(map(str, true_list))
    false_list_str = ",".join(map(str, false_list))

    memo_keys = list(MEMO.keys())
    if true_list_str in memo_keys:
        return MEMO[true_list_str]
    if false_list_str in memo_keys:
        return MEMO[false_list_str]

    if sum(true_list) == sum(false_list):
        MEMO[true_list_str] = MEMO[false_list_str] = True
        return True
    else:
        MEMO[true_list_str] = MEMO[false_list_str] = False
        return False


ANSWER = "impossible"


def comb(matrix, threshold, W):
    global ANSWER
    if len(matrix) > threshold:
        res = check_memo_and_jduge(matrix, W)
        if res:
            ANSWER = "possible"
        return
    for b in [True, False]:
        if ANSWER == "possible":
            return
        comb(matrix + [b], threshold, W)


comb([], N - 1, W)
print(ANSWER)