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
dp = [[INFTY for _ in range(N+1)] for _ in range(K)]
dp[0][S] = X[S]
for i in range(1,K):
    for j in range(1,N+1):
        for k,y in BG[j]:
            dp[i][j] = min(dp[i][j],dp[i-1][k]+y)
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))
ans = [S]
u = S
while u!=T:
    u = Pa[u]
    ans.append(u)
dmin = INFTY
indmin = T
for j in range(1,N+1):
    dist_ = dp[K-1][j]+dist[j]
    if dist_<dmin:
        dmin = dist_
        indmin = j
if dist[S]>=INFTY:
    print("Impossible")
elif 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:
        for v,y in BG[u]:
            if dp[k][u]==dp[k-1][v]+y:
                u = v
                k -= 1
                ans.append(u)
                break
    ans = ans[::-1]
    if indmin==T:
        print(len(ans))
        print(*ans)
    else:
        u = indmin
        while u!=T:
            u = Pa[u]
            ans.append(u)
        print(len(ans))
        print(*ans)
else:
    print("Impossible")