N = int(raw_input())
W = map(int,raw_input().split())
queue = [0,0,0]
ans = 0
while len(queue) > 0:
	i,a,b = queue.pop(),queue.pop(),queue.pop()
	if i == N and a == b:
		ans = 1
		break
	if i >= N:continue
	queue.append(i + 1)
	queue.append(a + W[i])
	queue.append(b)
	queue.append(i + 1)
	queue.append(a)
	queue.append(b + W[i])
if ans == 0:
	print 'impossible'
else:
	print 'possible'