@n = gets.to_i

def sol w,ans,memo,sum,limit
    if sum == limit
        ans[sum] = true
        return true
    elsif sum > limit
        return false
    end
    if ans[sum] != nil
        return ans[sum]
    end
    @n.times{|i|
        if !memo[i]
            memo[i] = true
            if sol(w,ans,memo,sum + w[i],limit)
                ans[sum] = true
                return true
            end
            memo[i] = false
        end
        }
    ans[sum] = false
    return false
end

w = gets.split.map(&:to_i).sort
sum = w.inject(:+)

if sum % 2 == 1
    puts 'impossible'
else
    limit = sum / 2
    ans = Array.new(limit + 1)
    memo = Array.new(@n,false)
    if sol(w,ans,memo,0,limit)
        puts 'possible'
    else
        puts 'impossible'
    end
end