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)]
g = [[] for _ in range(n+1)]
for a, b, c in abc:
    g[a].append((b, c))
    g[b].append((a, c))
s = [10**18+1]*(n+1)
for d, e in de:
    s[d] = e

import heapq
q = [(-y, 1)]

mx = [0]*(n+1)
mx[1] = y
ans = 0
while q:
    ny, nn = heapq.heappop(q)
    ny *= -1
    if ny < mx[nn]: continue
    ans = max(ans, ny//s[nn])
    for b, c in g[nn]:
        if mx[b] < ny - c:
            heapq.heappush(q, (c-ny, b))
            mx[b] = ny - c
print(ans)