#include<bits/stdc++.h>
using namespace std;

int main(){
	int n, l; cin >> n >> l;
	int a, b; cin >> a;
	for(int i = 1; i < n; ++i){
		cin >> b;
		if(a + b >= l){
			cout << "Possible\n";
			for(int j = 1; j < i; ++j) cout << j << endl;
			for(int j = n - 1; j > i; --j) cout << j << endl;
			cout << i << endl;
			return 0;
		}
		a = b;
	}
	cout << "Impossible\n";
	return 0;
}