#include <iostream>
using namespace std;
int main() {
	int a, b, k[100005], mon;
	cin >> a >> b;
	bool canunrap = false;
	for (int i = 0; i < a; ++i) {
		cin >> k[i];
		if (i != 0 && k[i] + k[i - 1] >= b) {
			canunrap = true;
			mon = i-1;
		}
	}
	if (!canunrap) {
		cout << "Impossible" << endl;
		return 0;
	}
	cout << "Possible" << endl;
	for (int i = 1; i <= mon; ++i) {
		cout << i << endl;
	}
	for (int i = a-1; i > mon; --i) {
		cout << i << endl;
	}
}