25

// Algo : BCC
            low[u] = min(low[u], low[v]);
            if (u != root && dis[u] <= low[v]) {
                total_node.clear();
                while (!BCC.empty()) {
                    int x = BCC.top().u;
                    int y = BCC.top().v;
                    cout << x << " " << y << endl;
                    BCC.pop();
                    if (x == u && y == v)
                        break;
                }
            }
        }
        else {
            low[u] = min(low[u], dis[v]);
        }
    }
}
void BCC_ALL() {
    memset(vis, 0, sizeof vis);
    for (int i = 0; i < tNode; i++) {
        if (vis[i])
            continue;
        timer = 1; child = 0; root = i;
        dfs(root);
        total_node.clear();
        while (!BCC.empty()) {
            int x = BCC.top().u;
            int y = BCC.top().v;
            cout << x << " " << y << endl;
            BCC.pop();
        }
    }
}

// Algorithm     : Havel Hakimi
// Complexity    : O(n^2 log(n))

int arr[mx], n;  // n : Number of Node
bool Havel_Hakimi() {
	for (int i=0; i<n-1; i++) {
		sort(arr+i, arr+n, greater <int> ());
		for (int j=i+1; j<=i+arr[i]; j++) {
			arr[j]--;
			if (arr[j] < 0) return false;
		}
	}
	if (arr[n-1] != 0) return false;
	return true;
}

int main() {
	while (cin >> n, n) {
		bool flag = true;
		int sumOfDegree = 0;
		for (int i=0; i<n; i++) {
			cin >> arr[i];
			if (arr[i] >= n || arr[i]<0)
				flag = false;
			sumOfDegree += arr[i];
		}
		if (sumOfDegree & 1)
			cout << "Not possible" << endl;
		else if (!flag || !Havel_Hakimi())
			cout << "Not possible" << endl;
		else
			cout << "Possible" << endl;
	}
	return 0;
}