#include <atcoder/lazysegtree.hpp> using namespace atcoder; #include <bits/stdc++.h> using namespace std; #define rep(i, n) for(int i=0; i<n; i++) #define chmin(x, y) x = min(x, y) #define chmax(x, y) x = max(x, y) // #include <all.hpp> #define int long long signed main() { int n, m, p, y; cin >> n >> m >> p >> y; vector<vector<pair<int, int>>> g(n); rep(i, m) { int a, b, c; cin >> a >> b >> c; a--; b--; g[a].push_back({b, c}); g[b].push_back({a, c}); } vector<int> dist(n, 1e18); dist[0] = 0; priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> pq; pq.push({0, 0}); while(!pq.empty()) { auto [d, v] = pq.top(); pq.pop(); if(dist[v] < d) continue; for(auto [nv, c] : g[v]) { if(dist[nv] > dist[v] + c) { dist[nv] = dist[v] + c; pq.push({dist[nv], nv}); } } } int ans = 0; rep(i, p) { int d, e; cin >> d >> e; d--; chmax(ans, (y - dist[d]) / e); } cout <<ans << endl; }