from collections import deque

n = int(input())
weights = sorted(list(map(int, input().split())), reverse=True)

d = deque(weights)
cursor = d.popleft()

while True:
    if len(d) == 0:
        break

    if cursor < 0:
        cursor += d.popleft()
    else:
        cursor -= d.pop()

if cursor == 0:
    print('possible')
else:
    print('impossible')