import sys
input = sys.stdin.readline
import heapq

N,S,T,K=map(int,input().split())
X=[0]+list(map(int,input().split()))
M=int(input())

E=[[] for i in range(N+1)]
for i in range(M):
    a,b,y=map(int,input().split())
    E[a].append((b,y))

DP=[1<<60]*(N+1)
FR=[-1]*(N+1)

DP[S]=X[S]
Q=[(X[S],S)]

while Q:
    time,ind=heapq.heappop(Q)
    if time>DP[ind]:
        continue

    for to,cost in E[ind]:
        if DP[to]>DP[ind]+X[to]+cost:
            DP[to]=DP[ind]+X[to]+cost
            FR[to]=ind
            heapq.heappush(Q,(DP[to],to))

if DP[T]==1<<60:
    print("Impossible")
    exit()

ANS=[]
now=T
while now!=-1:
    ANS.append(now)
    now=FR[now]

if len(ANS)>=K:
    print("Possible")
    print(DP[T])
    print(len(ANS))
    print(*ANS[::-1])
    exit()
else:
    print(ANS[1<<60])