// Source: https://usaco.guide/general/io #include <bits/stdc++.h> using namespace std; using ll = long long; #define eb emplace_back // faster than push_back xD // pbds UwU #include <ext/pb_ds/assoc_container.hpp> using namespace __gnu_pbds; #define oset tree<ll, null_type,less<ll>, rb_tree_tag,tree_order_statistics_node_update> // use pair for ms // my io library :D #define m1(x) template<class T, class... U> void x(T&& a, U&&... b) #define m2(x) (ll[]){(x forward<U>(b),0)...} m1(pr){cout << forward<T>(a); m2(cout << " " <<); cout << "\n";} m1(re){cin >> forward<T>(a); m2(cin >>);} const ll cap = 5e4+1; ll dist[cap]; vector<pair<ll,ll>> adj[cap]; void dijkstra(ll s){ priority_queue<pair<ll,ll>> pq; fill(dist, dist+cap, 1e18); pq.push({0, s}); dist[s] = 0; while (!pq.empty()){ pair<ll,ll> oknext = pq.top(); pq.pop(); oknext.first *= -1; for (auto u: adj[oknext.second]){ if (dist[oknext.second] + u.second < dist[u.first]){ dist[u.first] = dist[oknext.second] + u.second; pq.push({-dist[u.first], u.first}); } } } } int main() { ios::sync_with_stdio(0); cin.tie(0); ll k, n, m, o; re(k, n, m, o); for (ll i{}; i < m; i++){ ll a, b, t; re(a, b, t); adj[a].eb(make_pair(b, t)); } for (ll i{}; i < o; i++){ ll a, b; re(a, b); dijkstra(a); if (dist[b] == 1e18) pr(-1); else pr(dist[b]); } }