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() while True: buf = 0 cnt = 0 for i in range(0,len(list)): buf += W[i] * list[i] if buf not in ans: 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')