from heapq import heappush, heappop N, M, P, Y = map(int, input().split()) G = [[] for _ in range(N)] for _ in range(M): u, v, c = map(int, input().split()) G[u-1].append((v-1, c)) G[v-1].append((u-1, c)) DE = [list(map(int, input().split())) for _ in range(P)] def dijkstra(start): INF = 10**18 dist = [INF]*N dist[start] = 0 visited = [False]*N que = [(0, start)] while que: d, now = heappop(que) if visited[now]: continue visited[now] = True for next, weight in G[now]: if dist[now]+weight < dist[next]: dist[next] = dist[now]+weight heappush(que, (dist[next], next)) return dist dist = dijkstra(0) ans = 0 for D, E in DE: D -= 1 if Y-dist[D] >= 0: ans = max(ans, (Y-dist[D])//E) print(ans)