import heapq

INF = 1 << 60

n, s, t, k = map(int, input().split())
s -= 1
t -= 1
x = list(map(int, input().split()))

m = int(input())
edges = []
idx = {}
vs = [s, (k - 1) * n + t]
idx[vs[0]] = 0
idx[vs[1]] = 1
src = 0
dst = 1
for _ in range(m):
  a, b, y = map(int, input().split())
  a -= 1
  b -= 1
  for i in range(k):
    u = i * n + a
    v = min(i + 1, k - 1) * n + b
    if idx.get(u, None) is None:
      idx[u] = len(idx)
      vs.append(u)
    if idx.get(v, None) is None:
      idx[v] = len(idx)
      vs.append(v)

    edges.append((idx[u], idx[v], y + x[b]))

g = [[] for _ in range(len(idx))]
for u, v, w in edges:
  g[u].append((v, w))

dist = [INF for _ in range(len(idx))]
dist[src] = x[s]
prev = [None for _ in range(len(idx))]
hp = [(dist[src], src)]
while len(hp) > 0:
  cd, cur = heapq.heappop(hp)
  if cd > dist[cur]:
    continue

  for nxt, cost in g[cur]:
    if dist[cur] + cost < dist[nxt]:
      dist[nxt] = dist[cur] + cost
      prev[nxt] = cur
      heapq.heappush(hp, (dist[nxt], nxt))

if dist[dst] < INF:
  print("Possible")
  print(dist[dst])

  cur = dst
  order = []
  while not cur is None:
    order.append(vs[cur] % n + 1)
    cur = prev[cur]

  order.reverse()
  print(len(order))
  print(*order, sep=" ")
else:
  print("Impossible")