# your code goes here
n = input()
b = list(int(i) for i in input().split())
b.reverse()
N=sum(b)
e=1
def sca(e,r,i,ba):
    if e==0:
        return 0
    elif r-ba[i]==0:
        e=0
        return 0
    elif r-ba[i] < 0:
            return 1*sca(e,r,i+1,ba)
    elif len(ba)==1:
        return 1
    else:
        ba=ba.pop(i)
        print(ba)
        return 1*sca(e,r-b[i],i,ba)
if N/2!=int(N/2):
    print("impossible")
else:
    N=int(N/2)
    print(N)
    if sca(e,N,0,b)==0:
        print("possible")
    else:
        print("impossible")