n = int(input())
l = [int(x) for x in input().split()]
l.sort()
a = 0
b = 0
for i in range(n//2):
    a += l[i]
    b += l[-i]
if n % 2 != 0:
    if a < b:
        a += l[n//2+1]
    else:
        b += l[n//2+1]
if a == b:
    print('possible')
else:
    print('impossible')