#include <iostream>
#include <vector>
#include <stack>
#include <algorithm>

using namespace std;

int main()
{
	int N;
	cin >> N;

	vector<int> W(N);
	for(int i = 0 ; i < N; i++ ){
		cin  >> W[i];
	}
	sort( W.begin(), W.end() );
	int half = 0;
	for( auto x: W ) {
		half += x;
	}
	if( half%2 == 1 )  {
		cout << "impossible" << endl;
		return 0;
	}

	half = half / 2;

	// cout << "half " << half << endl;

	stack<int> s;

	int sum =0;
	int i = 0;
	while( 1 ) {
		if( i >= N ) {
			if( s.empty() ) {
				cout << "impossible" << endl;
				return 0;
			}
			i = s.top();
			sum -= W[i];
			i++;
			s.pop();
		}
		if( half == sum + W[i] ) {
			cout << "possible" << endl;
			while( s.empty() ) {
				cout << s.top() << endl;
				s.pop();
			}


			return 0;
		}
		else if( half >  sum + W[i] ) {
			sum += W[i];
			s.push( i );
			i++;
		}
		else if( half < sum + W[i] ) {
			if( s.empty() ) {
				cout << "impossible" << endl;
				return 0;
			}
			i = s.top();
			sum -= W[i];
			// cout << "W " << i << " " << W[i] << endl;
			s.pop();
			// i = s.top();
			i+=1;
		}
	}
	
	return 0;
}