from heapq import *

n,s,t,k = map(int,input().split())
s,t = s-1,t-1
X = list(map(int,input().split()))
m = int(input())
e = [[] for i in range(n)]
for i in range(m):
    a,b,y = map(int,input().split())
    e[a-1].append((b-1,y))


inf = 10**20
dis = [[inf]*k for i in range(n)]
par = [[[-1,-1]for _ in range(k) ]for i in range(n)]
dis[s][0] = X[s]
h = [(X[s],s,0)]

while h:
    d,now,l = heappop(h)
    if now == t and l == k-1:
        print("Possible")
        print(d)
        ans = []
        while now != -1:
            ans.append(now+1)
            now,l = par[now][l]
        print(len(ans))
        print(*ans[::-1])
        exit()
    if d != dis[now][l]:
        continue
    for nex, y in e[now]:
        nd = d+y+X[nex]
        nl = min(l+1,k-1)
        if dis[nex][nl] > nd:
            dis[nex][nl] = nd
            heappush(h,(nd,nex,nl))
            par[nex][nl] = [now,l]
print("Impossible")