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
dist1 = [INFTY for _ in range(N+1)]
visited = [False for _ in range(N+1)]
dist1[S] = X[S]
heap = [(X[S],S)]
while heap:
    d,j = heapq.heappop(heap)
    if d>dist1[j]:continue
    visited[j] = True
    for k,y in G[j]:
        if visited[k]:continue
        if dist1[k]>d+y:
            dist1[k] = d+y
            heapq.heappush(heap,(d+y,k))
ans1 = [T]
u = T
while u!=S:
    for v,y in BG[u]:
        if dist1[u]==dist1[v]+y:
            ans1.append(v)
            u = v
            break
ans1 = ans1[::-1]
dist2 = [[INFTY for _ in range(N+1)] for _ in range(K+1)]
visited = [[False for _ in range(N+1)] for _ in range(K+1)]
dist2[0][S] = X[S]
heap = [(X[S],0,S)]
while heap:
    d,i,j = heapq.heappop(heap)
    if d>dist2[i][j]:continue
    visited[i][j] = True
    if i==K:continue
    for k,y in G[j]:
        if visited[i+1][k]:continue
        if dist2[i+1][k]>d+y:
            dist2[i+1][k] = d+y
            heapq.heappush(heap,(d+y,i+1,k))
dist3 = [INFTY for _ in range(N+1)]
visited = [False for _ in range(N+1)]
dist3[T] = 0
heap = [(0,T)]
while heap:
    d,j = heapq.heappop(heap)
    if dist3[j]<d:continue
    visited[j] = True
    for k,y in BG[j]:
        if visited[k]:continue
        if dist3[k]>d+y:
            dist3[k] = d+y
            heapq.heappush(heap,(d+y,k))
dmin = INFTY
indmin = T
for j in range(1,N+1):
    dist_ = dist2[K-1][j]+dist3[j]
    if dist_<dmin:
        dmin = dist_
        indmin = j
if dist1[T]>=INFTY:
    print("Impossible")
elif len(ans1)>=K:
    print("Possible")
    print(dist1[T])
    print(len(ans1))
    print(*ans1)
elif dmin<INFTY:
    print("Possible")
    print(dmin)
    ans = [indmin]
    u = indmin
    k = K-1
    while k>0:
        for v,y in BG[u]:
            if dist2[k][u]==dist2[k-1][v]+y:
                ans.append(v)
                u = v
                k -= 1
                flag = True
                break
    ans = ans[::-1]
    if indmin==T:
        print(len(ans))
        print(*ans)
    else:
        u = indmin
        while u!=T:
            for v,y in G[u]:
                if dist3[u]==dist3[v]+y:
                    ans.append(v)
                    u = v
                    break
        print(len(ans))
        print(*ans)
else:
    print("Impossible")