import sys

sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.buffer.readline())
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def LI1(): return list(map(int1, sys.stdin.buffer.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def BI(): return sys.stdin.buffer.readline().rstrip()
def SI(): return sys.stdin.buffer.readline().rstrip().decode()
dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = 10**16
# md = 998244353
# md = 10**9+7

from heapq import *

n, s, t, k = LI()
s, t = s-1, t-1
xx = LI()
m = II()
to = [[] for _ in range(n)]
for _ in range(m):
    u, v, c = LI1()
    to[u].append((v, c+1))

dist = [[inf]*k for _ in range(n)]
pre = [[(-1, -1) for _ in range(k)] for _ in range(n)]
dist[s][0] = xx[s]
hp = [(xx[s], s, 0)]
while hp:
    d, u, f = heappop(hp)
    if u == t and f == k-1:
        print("Possible")
        print(d)
        pp = []
        while u != -1:
            pp.append(u+1)
            u, f = pre[u][f]
        print(len(pp))
        print(*pp[::-1])
        exit()
    if d > dist[u][f]: continue
    for v, c in to[u]:
        nd = d+c+xx[v]
        nf = min(f+1, k-1)
        if nd >= dist[v][nf]: continue
        dist[v][nf] = nd
        pre[v][nf] = (u, f)
        heappush(hp,(nd,v,nf))

print("Impossible")