//----------vahagng----------//
#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
// #include <ext/pb_ds/assoc_container.hpp>
using namespace std;
// using namespace __gnu_pbds;
// template <class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#ifndef ONLINE_JUDGE
#define dbg(x) cerr << #x <<" "; print(x); cerr << endl;
#else
#define dbg(x)
#endif
void print(long long t) { cerr << t; }
void print(int t) { cerr << t; }
void print(string t) { cerr << t; }
void print(char t) { cerr << t; }
void print(double t) { cerr << t; }
void print(long double t) { cerr << t; }
void print(unsigned long long t) { cerr << t; }
template <class T, class V> void print(pair <T, V> p);
template <class T> void print(vector <T> v);
template <class T> void print(set <T> v);
template <class T, class V> void print(map <T, V> v);
template <class T> void print(multiset <T> v);
template <class T, class V> void print(T v[], V n) { cerr << "["; for (int i = 0; i < n; i++) { cerr << v[i] << " "; } cerr << "]"; }
template <class T, class V> void print(pair <T, V> p) { cerr << "{"; print(p.first); cerr << ","; print(p.second); cerr << "}"; }
template <class T> void print(vector <T> v) { cerr << "[ "; for (T i : v) { print(i); cerr << " "; } cerr << "]"; }
template <class T> void print(set <T> v) { cerr << "[ "; for (T i : v) { print(i); cerr << " "; } cerr << "]"; }
template <class T> void print(unordered_set <T> v) { cerr << "[ "; for (T i : v) { print(i); cerr << " "; } cerr << "]"; }
template <class T> void print(multiset <T> v) { cerr << "[ "; for (T i : v) { print(i); cerr << " "; } cerr << "]"; }
template <class T, class V> void print(map <T, V> v) { cerr << "[ "; for (auto i : v) { print(i); cerr << " "; } cerr << "]"; }
#define ll long long
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define ld long double
#define sz(v) v.size()
#define endl '\n'
#define stress_test freopen("out.txt", "r", stdin); freopen("in.txt", "w", stdout);
const ll inf = 8e18, mod = 1e9 + 7, mod2 = 998244353;
void SetIO(string str = "") {
if (str != "") {
freopen((str + ".in").c_str(), "r", stdin);
freopen((str + ".out").c_str(), "w", stdout);
}
else {
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
}
}
void FastIO() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
}
// mt19937 rnd(chrono::system_clock::now().time_since_epoch().count());
const int N = 1e5 + 10, sq = 500, M = 2e5 + 10, Q = pow(3, 7);
ll n, k, m, q, dp[N];
vector<pair<int, ll>> adj[N], rev_adj[N];
void solve(int tc) {
cin >> k >> n >> m >> q;
for(int i = 0; i < m; i++){
int u, v;
ll w;
cin >> u >> v >> w;
adj[u].push_back({v, w});
rev_adj[v].push_back({u, w});
}
for(int i = 0; i <= n; i++){
dp[i] = inf;
assert(adj[i].size() <= k);
}
while(q--){
int u, v;
cin >> u >> v;
if(u / k > v / k){
cout << -1 << endl;
continue;
}
for(int i = u; i <= v; i++){
dp[i] = inf;
}
dp[u] = 0;
priority_queue<pair<ll, int>, vector<pair<ll, int>>, greater<pair<ll,int>>> pq;
pq.push({0, u});
while(!pq.empty()){
auto [d, node] = pq.top();
pq.pop();
if(d != dp[node]) continue;
if(node / k == v / k) continue;
for(auto [i, w] : adj[node]){
if(dp[i] > dp[node] + w){
dp[i] = dp[node] + w;
if(i / k != v / k) pq.push({dp[i], i});
}
}
}
cout << (dp[v] == inf ? -1 : dp[v]) << endl;
}
}
void precalc() {
}
int main() {
// SetIO("in");
// stress_test;
FastIO();
int test_case = 1;
// cin >> test_case;
auto start = chrono::steady_clock::now();
precalc();
int cnt = 1;
while (test_case--) {
solve(cnt++);
}
auto end = chrono::steady_clock::now();
std::chrono::duration<double> elapsed_seconds = end - start;
cerr << "Execution: " << elapsed_seconds.count() << endl;
return 0;
}
