from heapq import *

N, M, P, Y = map(int, input().split())
ABC = [list(map(int, input().split())) for _ in range(M)]
DE = [list(map(int, input().split())) for _ in range(P)]
E = [[] for _ in range(N)]
for a, b, c in ABC:
    a -= 1
    b -= 1
    E[a].append((b, c))
    E[b].append((a, c))

INF = 10 ** 16
D = [INF] * N


# 普通のダイクストラ
def dijkstra():
    D[0] = 0
    q = [(0, 0)]
    while q:
        d, u = heappop(q)
        # 下のifでTLE解消することがある
        if d > D[u]: continue
        for i in E[u]:
            a, b = i
            if D[a] > D[u] + b:
                D[a] = D[u] + b
                heappush(q, (D[a], a))
    return

dijkstra()
ans = 0
for d, e in DE:
    d -= 1
    ans = max(ans, (Y - D[d]) // e)

print(ans)