// #include #include using namespace std; using ll = long long; constexpr ll inf = (1LL << 61); ll dx[4] = {0, 1, 0, -1}; ll dy[4] = {-1, 0, 1, 0}; #define rep(i, n) for (ll i = 0; i < (ll)(n); ++i) #define REP(i, init, n) for (ll i = (ll)init; i < (ll)(n); ++i) // ll op(ll a, ll b) { return max(a, b); } // ll e() { return -inf; } ll a[200010], b[200010], c[200010], d[200010], e[200010]; ll Q[200010]; int main() { ll n, m, p, y; cin >> n >> m >> p >> y; vector>> g(n); rep(i, m) { cin >> a[i] >> b[i] >> c[i]; g[a[i] - 1].push_back({b[i] - 1, c[i]}); g[b[i] - 1].push_back({a[i] - 1, c[i]}); } rep(i, p) { cin >> d[i] >> e[i]; Q[d[i] - 1] = e[i]; } using P = pair; priority_queue, greater<>> pq; vector dist(n, inf); pq.push({0, 0}); dist[0] = 0; while (pq.size()) { auto [di, v] = pq.top(); pq.pop(); if (dist[v] < di) continue; for (auto& [to, cost] : g[v]) { if (di + cost < dist[to]) { dist[to] = di + cost; pq.push({dist[to], to}); } } } ll ans = 0; rep(i, n) { if (Q[i] != 0) { auto R = max(y - dist[i], 0ll); ans = max(ans, R / Q[i]); } } cout << ans << endl; }