class Heap_Point:
        def __init__(self,x,d):
            self.d=d
            self.x=x

        def __str__(self):
            return "(point:{}, dist:{})".format(self.x,self.d)

        def __repr__(self):
            return str(self)

        def __lt__(self,other):
            return self.d<other.d

        def __iter__(self):
            yield from (self.x,self.d)
#================================================
import sys
from heapq import heapify,heappop,heappush

input=sys.stdin.readline
N,S,T,K=map(int,input().split())
X=["*"]+list(map(int,input().split()))

M=int(input())
E=[[] for _ in range(N+1)]
for _ in range(M):
    A,B,Y=map(int,input().split())
    E[A].append((B,Y))

inf=float("inf")

DP=[[inf]*(K+1) for _ in range(N+1)]
DP[S][1]=X[S]

Reverse=[[(0,0) for _ in range(K+1)] for _ in range(N+1)]

Q=[Heap_Point((S,1),0)]
heapify(Q)

while Q:
    (x,k),d=heappop(Q)

    if DP[x][k]<d:
        continue

    if x==T and k==K:
        break

    l=min(k+1,K)
    for y,m in E[x]:
        if DP[x][k]+m+X[y]<DP[y][l]:
            DP[y][l]=DP[x][k]+m+X[y]
            Reverse[y][l]=(x,k)
            heappush(Q,Heap_Point((y,l),DP[y][l]))

V=DP[T][K]

if V<inf:
    x,k=T,K
    P=[]

    while k>0:
        P.append(x)
        x,k=Reverse[x][k]

    print("Possible")
    print(V)
    print(len(P))
    print(*P[::-1])
else:
    print("Impossible")