import std.stdio, std.conv, std.functional, std.string;
import std.algorithm, std.array, std.container, std.range, std.typecons;
import std.bigint, std.numeric, std.math, std.random;
import core.bitop;

string FMT_F = "%.10f";

static File _f;
void file_io(string fn) { _f = File(fn, "r"); }
static string[] s_rd;
T _RD(T = long)() { while(!s_rd.length) s_rd = readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
T _RD(T = long)(File f) { while(!s_rd.length) s_rd = f.readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
T[] _RDA(T = long)(T fix = 0) { auto r = readln.chomp.split.to!(T[]); r[] += fix; return r; }
T[] _RDA(T = long)(File f, T fix = 0) { auto r = f.readln.chomp.split.to!(T[]); r[] += fix; return r; }
T RD(T = long)() { if (_f.isOpen) return _RD!T(_f); else return _RD!T; }
T[] RDA(T = long)(T fix = 0) { if (_f.isOpen)  return _RDA!T(_f, fix); else return _RDA!T(fix); }

size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;}
size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; }

void chmin(T)(ref T x, T y) { x = min(x, y); } void chmax(T)(ref T x, T y) { x = max(x, y); }
bool inside(T)(T x, T b, T e) { return x >= b && x < e; }
T lcm(T)(T x, T y) { return x * (y / gcd(x, y)); }
double[] rotate(double[] vec, double rad) { return [cos(rad)*vec[0] - sin(rad)*vec[1], sin(rad)*vec[0] + cos(rad)*vec[1]]; }

//long mod = 10^^9 + 7;
long mod = 998_244_353;
//long mod = 1_000_003;
void moda(ref long x, long y) { x = (x + y) % mod; }
void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; }
void modm(ref long x, long y) { x = (x * y) % mod; }
void modpow(ref long x, long y) { if (!y) { x = 1; return; } auto t = x; x.modpow(y>>1); x.modm(x); if (y&1) x.modm(t); }
void modd(ref long x, long y) { y.modpow(mod - 2); x.modm(y); }

void main()
{
	auto N = RD;
	auto S = RD-1;
	auto T = RD-1;
	auto K = RD;
	auto X = RDA;
	auto M = RD;
	auto edges = new long[][][](N);
	foreach (i; 0..M)
	{
		auto A = RD-1;
		auto B = RD-1;
		auto Y = RD;
		edges[A] ~= [B, Y];
	}

	auto dist = new long[][](N, K+N);
	foreach (i; 0..N)
		dist[i][] = long.max;
	dist[S][0] = X[S];
	BinaryHeap!(Array!(long[]), "a[2] > b[2]") q;
	q.insert([S, 0, X[S]]);
	auto par = new long[][](N, K+N);
	long[] ans;
	while (!q.empty)
	{
		auto nd = q.front; q.removeFront;
		auto u1 = nd[0];
		auto u2 = nd[1];
		auto c = nd[2];
		if (u1 == T && u2 >= K-1)
		{
			ans = [u2, c];
			break;
		}
		foreach (e; edges[u1])
		{
			auto v1 = e[0];
			auto v2 = min(u2+1, K+N-1);
			auto d = c + X[v1] + e[1];
			if (d < dist[v1][v2])
			{
				dist[v1][v2] = d;
				par[v1][v2] = u1;
				debug writeln("v1:", v1, " v2:", v2, " u1:", u1, " d:", d);
				q.insert([v1, v2, d]);
			}
		}
	}
	debug writeln(dist);
	debug writeln(par);

	if (ans.empty)
		writeln("Impossible");
	else
	{
		writeln("Possible");
		writeln(ans[1]);
		auto pos = [T, ans[0]];
		auto arr = [T+1];
		while (pos[1] != 0)
		{
			pos = [par[pos[0]][pos[1]], pos[1]-1];
			arr ~= pos[0]+1;
		}
		arr.reverse;
		writeln(arr.length);
		arr.map!(to!string).join(" ").writeln;
	}
	stdout.flush;
	debug readln;
}