#include <iostream>
#include <vector>
#include <queue>
#include <functional>
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;
int from_level = a / K;
int to_level = b / K;
if (to_level == from_level + 1) {
graph[a].emplace_back(b, c);
}
}
auto dijkstra = [&](int start, int goal) {
vector<int> dist(N, INF);
priority_queue<pair<int, int>, vector<pair<int, int>>, greater<>> pq;
dist[start] = 0;
pq.emplace(0, start);
while (!pq.empty()) {
auto [d, u] = pq.top(); pq.pop();
if (d > dist[u]) continue;
if (u == goal) return dist[u];
for (auto &[v, cost] : graph[u]) {
if (dist[v] > dist[u] + cost) {
dist[v] = dist[u] + cost;
pq.emplace(dist[v], v);
}
}
}
return -1;
};
for (int i = 0; i < O; ++i) {
int a, b;
cin >> a >> b;
int result = dijkstra(a, b);
cout << result << '\n';
}
return 0;
}
