import std.stdio;
import std.algorithm;
import std.string;
import std.range;
import std.array;
import std.conv;
import std.complex;
import std.math;
import std.ascii;
import std.bigint;
import std.container;
import std.typecons;

auto readInts() {
	return array(map!(to!int)(readln().strip().split()));
}
auto readInt() {
	return readInts()[0];
}
auto readLongs() {
	return array(map!(to!long)(readln().strip().split()));
}
auto readLong() {
	return readLongs()[0];
}

void readlnTo(T...)(ref T t) {
    auto s = readln().split();
    assert(s.length == t.length);
    foreach(ref ti; t) {
        ti = s[0].to!(typeof(ti));
        s = s[1..$];
    }
}

const real eps = 1e-10;

void main(){
    long n, l;
    readlnTo(n, l);
    auto a = readLongs();
    long[] b;
    foreach(i; iota(n-1)) {
        b ~= a[i] + a[i+1];
    }
    if(reduce!((a,b) => a > b ? a: b)(0L, b) < l) {
        writeln("Impossible");
        return;
    }
    writeln("Possible");
    long idx = 0;
    while(b[idx] < l) {
        ++idx;
    }
    long[] ans;
    foreach(i; iota(idx, n-1)) {
        ans ~= i+1;
    }
    foreach_reverse(i; iota(idx)) {
        ans ~= i+1;
    }
    foreach_reverse(ai; ans) {
        writeln(ai);
    }
}

