import heapq
N,S,T,K = map(int,input().split())
X = [0]+list(map(int,input().split()))
M = int(input())
G = {i:[] for i in range(1,N+1)}
BG = {i:[] for i in range(1,N+1)}
for _ in range(M):
    a,b,y = map(int,input().split())
    G[a].append((b,y+X[b]))
    BG[b].append((a,y+X[b]))
INFTY = 10**15
dist2 = [[[INFTY,0] for _ in range(N+1)] for _ in range(K)]
visited = [[False for _ in range(N+1)] for _ in range(K)]
dist2[0][S][0] = X[S]
heap = [(X[S],0,S)]
while heap:
    d,i,j = heapq.heappop(heap)
    if visited[i][j] or d>dist2[i][j][0]:continue
    visited[i][j] = True
    if i==K-1:continue
    for k,y in G[j]:
        if visited[i+1][k]:continue
        if dist2[i+1][k][0]>d+y:
            dist2[i+1][k][0] = d+y
            dist2[i+1][k][1] = (i,j)
            heapq.heappush(heap,(d+y,i+1,k))
dist3 = [[INFTY,0] for _ in range(N+1)]
visited = [False for _ in range(N+1)]
dist3[T][0] = 0
heap = [(0,T)]
while heap:
    d,j = heapq.heappop(heap)
    if visited[j] or dist3[j][0]<d:continue
    visited[j] = True
    for k,y in BG[j]:
        if visited[k]:continue
        if dist3[k][0]>d+y:
            dist3[k][0] = d+y
            dist3[k][1] = j
            heapq.heappush(heap,(d+y,k))
ans3 = [S]
u = S
while u!=T:
    u = dist3[u][1]
    ans3.append(u)
dmin = INFTY
indmin = T
for j in range(1,N+1):
    dist_ = dist2[K-1][j][0]+dist3[j][0]
    if dist_<dmin:
        dmin = dist_
        indmin = j
if dist3[S][0]>=INFTY:
    print("Impossible")
elif len(ans3)>=K:
    print("Possible")
    print(dist3[S][0]+X[S])
    print(len(ans3))
    print(*ans3)
elif dmin<INFTY:
    print("Possible")
    print(dmin)
    ans = [indmin]
    u = indmin
    k = K-1
    while k>0:
        k,u = dist2[k][u][1]
        ans.append(u)
    ans = ans[::-1]
    if indmin==T:
        print(len(ans))
        print(*ans)
    else:
        u = indmin
        while u!=T:
            u = dist3[u][1]
            ans.append(u)
        print(len(ans))
        print(*ans)
else:
    print("Impossible")