N = int(raw_input())
a = [int(x) for x in raw_input().split(' ')]

sorteda = sorted(a)

maxlen = sorteda[-1]
numpathsoflen = {}
if(sorteda[0] < (maxlen+1)/2):
    print 'Impossible'
elif(maxlen % 2 == 0 
     and sorteda[0] == maxlen/2 
     and sorteda[0] == sorteda[1]):
    print 'Impossible'
else:
    numnodes = maxlen + 1
    for i in range(N):
        if a[i] in numpathsoflen.keys():
            if numpathsoflen[a[i]] >= 2:
                numnodes += 1
            numpathsoflen[a[i]] += 1            
        else:
            numpathsoflen[a[i]] = 1
    if(numnodes != N):
        print 'Impossible'
    else:
        out= 'Possible'
        starti = (maxlen+1)/2 
        if maxlen % 2 == 0:
            starti += 1
        for i in range(starti, maxlen+1):
            if((not i in numpathsoflen.keys()) or numpathsoflen[i] < 2):
                out = 'Impossible'                
        print out