#include <bits/stdc++.h>

using namespace std;

int main() {
	int N,sum=0,ave=0;
	cin >> N;
	vector<int> W(N);

	vector<int> existance(10000);
	for (size_t i = 0; i < N; i++)
	{
		cin >> W.at(i);
		sum += W.at(i);
		existance.at(W.at(i)) ++;

	}
	if (sum%2||W.at(N-1)>sum/2)
	{
		cout << "impossible";
		return 0;
	}
	ave = sum / 2;
	for (size_t i = 0; i <= ave; i++)
	{
		for (size_t j = 1; j <i ; j++)
		{
			if (existance.at(j)*(existance.at(i-j)))
			{
				if (i/2!=j||existance.at(j)>1)
				{
					existance.at(i) += min(existance.at(i-j), existance.at(j));
				}
			}
		}
	}
	
	if (existance.at(ave)) cout << "possible";
	else cout << "impossible";
}