//Huyduocdithitp
#include <bits/stdc++.h>
using namespace std;
typedef int ll;
#define endl '\n'
#define faster ios::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
const ll INF = (ll)1e18;
const int N = 50004;
struct Query { ll u, v; } qr[N];
ll k, n, m, q;
ll kq[N];
vector<pair<ll,ll>> adj[N];
set<ll> mp1[N], mp2[N];
ll mx = 0;
map<ll, ll> state[N];
int main() {
faster;
cin >> k >> n >> m >> q;
mx = n / k;
for (int i = 1; i <= m; i++) {
ll u, v, w;
cin >> u >> v >> w;
adj[u].push_back({v, w});
}
for (int i = 1; i <= q; i++) {
cin >> qr[i].u >> qr[i].v;
if (qr[i].u / k >= qr[i].v / k) {
kq[i] = -1;
} else {
kq[i] = INF;
mp1[qr[i].u].insert(i);
mp2[qr[i].v].insert(i);
}
}
for (int id = 0; id <= mx; id++) {
int L = id * k;
int R = min<ll>(n, (id + 1) * k);
for (int u = L; u <= R; u++) {
// process queries ending at u
for (auto it : mp2[u]) {
auto itState = state[u].find(it);
if (itState != state[u].end()) {
kq[it] = min(kq[it], itState->second);
state[u].erase(itState);
}
}
// add queries starting at u
for (auto it : mp1[u]) {
state[u][it] = 0;
}
// relax along outgoing edges
for (auto &edge : adj[u]) {
ll v = edge.first;
ll w = edge.second;
for (auto &pr : state[u]) {
ll qi = pr.first;
ll val = pr.second + w;
auto it2 = state[v].find(qi);
if (it2 == state[v].end()) state[v][qi] = val;
else it2->second = min(it2->second, val);
}
}
state[u].clear();
}
}
for (int i = 1; i <= q; i++) {
cout << (kq[i] >= INF ? -1 : kq[i]) << endl;
}
return 0;
}
