import std.stdio, std.string, std.conv;
import std.algorithm, std.array;
 
void main()
{
    for(string s_; (s_=readln.chomp()).length;)
    {
        auto NL = s_.split.map!(to!int);
        immutable N=NL[0], L=NL[1];
        immutable a = readln.split.map!(to!int).array();
        int k=0,m=-1;
        foreach(i;1..N) if(m<a[i-1]+a[i]) k=i,m=a[i-1]+a[i];
        if(m<L) writeln("Impossible");
        else
        {
            writeln("Possible");
            foreach(i;1..k) writeln(i);
            foreach_reverse(i;k+1..N) writeln(i);
            writeln(k);
        }
    }
}