import heapq
N,S,T,K = map(int,input().split())
X = [0]+list(map(int,input().split()))
M = int(input())
BG = {i:[] for i in range(1,N+1)}
for _ in range(M):
    a,b,y = map(int,input().split())
    BG[b].append((a,y+X[b]))
INFTY = 10**15
dp = [[INFTY for _ in range(N+1)] for _ in range(2)]
P = {}
dp[0][S] = X[S]
for i in range(1,K):
    for j in range(1,N+1):
        dp[i%2][j] = INFTY
        for k,y in BG[j]:
            if dp[i%2][j] > dp[(i-1)%2][k]+y:
                dp[i%2][j] = dp[(i-1)%2][k]+y
                P[(i,j)]=(i-1,k)
dist = [INFTY for _ in range(N+1)]
Pa = [0]*(N+1)
visited = [False for _ in range(N+1)]
dist[T] = 0
heap = [(0,T)]
while heap:
    d,j = heapq.heappop(heap)
    if visited[j] or dist[j]<d:continue
    visited[j] = True
    for k,y in BG[j]:
        if visited[k]:continue
        if dist[k]>d+y:
            dist[k] = d+y
            Pa[k] = j
            heapq.heappush(heap,(d+y,k))
dmin = INFTY
indmin = T
for j in range(1,N+1):
    dist_ = dp[(K-1)%2][j]+dist[j]
    if dist_<dmin:
        dmin = dist_
        indmin = j
if dist[S]>=INFTY:
    print("Impossible")
else:
    ans = [S]
    u = S
    while u!=T:
        u = Pa[u]
        ans.append(u)
    if len(ans)>=K:
        print("Possible")
        print(dist[S]+X[S])
        print(len(ans))
        print(*ans)
    elif dmin<INFTY:
        print("Possible")
        print(dmin)
        ans = [indmin]
        u = indmin
        k = K-1
        while k>0:
            k,u = P[(k,u)]
            ans.append(u)
        ans = ans[::-1]
        u = indmin
        while u!=T:
            u = Pa[u]
            ans.append(u)
        print(len(ans))
        print(*ans)
    else:
        print("Impossible")