#include <iostream>
#include <vector>
#include <queue>
#include <unordered_map>
#include <climits>
using namespace std;
const int INF = 1e9;
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int K, N, M, O;
cin >> K >> N >> M >> O;
vector<vector<pair<int, int>>> graph(N);
for (int i = 0; i < M; ++i) {
int a, b, c;
cin >> a >> b >> c;
if (b / K == a / K + 1) {
graph[a].emplace_back(b, c);
}
}
vector<vector<int>> dist(N, vector<int>(N, INF));
auto dijkstra = [&](int start) {
vector<int> local_dist(N, INF);
priority_queue<pair<int, int>, vector<pair<int, int>>, greater<>> pq;
local_dist[start] = 0;
pq.emplace(0, start);
while (!pq.empty()) {
auto [d, u] = pq.top();
pq.pop();
if (d > local_dist[u]) continue;
for (auto &[v, cost] : graph[u]) {
if (local_dist[v] > local_dist[u] + cost) {
local_dist[v] = local_dist[u] + cost;
pq.emplace(local_dist[v], v);
}
}
}
dist[start] = local_dist;
};
for (int i = 0; i < N; ++i) {
dijkstra(i);
}
for (int i = 0; i < O; ++i) {
int a, b;
cin >> a >> b;
if (dist[a][b] == INF) {
cout << -1 << '\n';
} else {
cout << dist[a][b] << '\n';
}
}
return 0;
}
