N = int(input())
V = list(map(int, input().split()))

total = sum(V)
han = total // 2
if total % 2 == 1: print("impossible")
else:
    done = [[0 for i in range(han)] for j in range(N+1)]
    done[N][0] = 1
    for i in range(N):
        for u in range(han):
            if u < V[i] - 1: done[i][u] = done[i-1][u]
            else: done[i][u] = max(done[i-1][u-V[i]+1], done[i-1][u])
    if done[N-1][han-1] == 1: print("possible")
    else: print("impossible")