#include <iostream>
#include <cmath>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <list>
#include <deque>
#include <algorithm>
#include <iomanip>
#include <functional>
#include <numeric>
#include <sstream>

#define REP(i, n) for(int i = 0;i < (n); i++)
#define REP2(i, x, n) for(int i = (x); i < (n); i++)
#define RREP(i, n) for (int i = (n) -1;i >= 0; i--)

#define ALL(a) (a).begin(),(a).end()
#define SORT(c) sort((c).begin(),(c).end())
#define DESCSORT(c) sort(c.begin(), c.end(), greater<int>())

#define LL long long int
#define LD long double

#define PI 3.14159265358979

using namespace std;

//================================================

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	int N;
	cin >> N;

	vector<int>vec(N);
	REP(i, N) {
		cin >> vec[i];
	}

	SORT(vec);
	int sum = accumulate(vec.begin(), vec.end(), 0);

	string ans = "impossible";
	vector<int>dp(10105);

	dp[0] = vec[0]; dp[1] = vec[1];
	REP2(i, 2, N + 1) {
		int a = dp[i - 1] + dp[i - 2];
		if (0 == (sum - a) - a) {
			ans = "possible";
			break;
		} else {
			dp[i] = (sum - a) - a;
		}
	}
	cout << ans << "\n";
	return 0;
}