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()



DP=[[1<<60]*(N+1) for i in range(K)]
FR=[[-1]*(N+1) for i in range(K)]

DP[0][S]=X[S]

for i in range(K-1):
    for j in range(1,N+1):
        if DP[i][j]==1<<60:
            continue

        for to,cost in E[j]:
            if DP[i+1][to]>DP[i][j]+cost+X[to]:
                DP[i+1][to]=DP[i][j]+cost+X[to]
                FR[i+1][to]=j

ANSX=DP[K-1][T]

DP=DP[K-1]
FR2=[-1]*(N+1)

Q=[]

for i in range(N+1):
    Q.append((DP[i],i))

heapq.heapify(Q)

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
            FR2[to]=ind
            heapq.heappush(Q,(DP[to],to))

if DP[T]==1<<60:
    print("Impossible")
    exit()
elif ANSX<=DP[T]:
    print("Possible")
    print(ANSX)
    ANS=[T]
    for j in range(K-1,0,-1):
        ANS.append(FR[j][ANS[-1]])
    print(len(ANS))
    print(*ANS[::-1])
    
else:
    print("Possible")
    print(DP[T])
    ANS=[T]
    now=T
    while now!=-1 and DP[FR2[now]]<DP[now]:
        now=FR2[now]
        ANS.append(now)

    for j in range(K-1,0,-1):
        ANS.append(FR[j][ANS[-1]])

    print(len(ANS))
    print(*ANS[::-1])