import sys

N = int(input())
W = input().split(' ')
median = 0
list = []
ans = []

for i in range(0,len(W)):
	W[i] = int(W[i])
	median += W[i]
	list.append(0)

if median % 2 == 1:
	print('impossible')
	sys.exit()

median = median // 2

W.sort.reverse()

while True:
	buf = 0
	cnt = 0
	flag = True
	
	for i in range(0,len(list)):
		buf += W[i] * list[i]
		if buf > median:
			flag = False
			break

	if buf not in ans and flag == True:
		ans.append(buf)

	while True:		
		if len(list) > 0:
			cnt += 1
			buf = list.pop()
			
			if buf != 1:
				break
			
		else:
			break
	if cnt == N and buf == 1:
		break
	
	list.append(1)
	cnt -= 1

	for i in range(0,cnt):
		list.append(0)

#print(ans)

if median in ans:
	print('possible')
else:
	print('impossible')