#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9;
int K, N, M, O;
vector<vector<pair<int, int>>> graph;
unordered_map<int, vector<int>> dist_cache;
vector<int>& dijkstra(int s) {
vector<int>& dist = dist_cache[s];
dist.assign(N, INF);
dist[s] = 0;
priority_queue<pair<int, int>, vector<pair<int, int>>, greater<>> pq;
pq.push({0, s});
while (!pq.empty()) {
auto [d, u] = pq.top(); pq.pop();
if (d > dist[u]) continue;
for (auto& [v, cost] : graph[u]) {
if (dist[v] > d + cost) {
dist[v] = d + cost;
pq.push({dist[v], v});
}
}
}
return dist;
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> K >> N >> M >> O;
graph.resize(N);
for (int i = 0; i < M; ++i) {
int a, b, t;
cin >> a >> b >> t;
if (b / K == (a / K) + 1)
graph[a].emplace_back(b, t);
}
while (O--) {
int a, b;
cin >> a >> b;
if (!dist_cache.count(a)) dist_cache[a].resize(N);
vector<int>& d = dist_cache[a][0] ? dist_cache[a] : dijkstra(a);
int res = d[b];
cout << (res == INF ? -1 : res) << '\n';
}
}
