// #pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
#define el "\n"
#define pii pair<int, int>
#define pll pair<ll, ll>
#define fi first
#define se second
#define mp make_pair
#define sqr(x) ((x) * (x))
#define FOR(i, l, r) for (int i = l; i <= (r); i++)
#define FOD(i, l, r) for (int i = l; i >= (r); i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define sz(x) ((int)(x).size())
#define fast_io ios_base::sync_with_stdio(false); cin.tie(nullptr);
using db = long double;
using ll = long long;
using ull = unsigned long long;
using vi = vector<int>;
using vll = vector<ll>;
using vpii = vector<pii>;
using vpll = vector<pll>;
using vvi = vector<vi>;
using vvll = vector<vll>;
using vbool = vector<bool>;
using vvbool = vector<vbool>;
template<class T> inline bool chmax(T &a, T const &b) { return (a < b ? (a = b, true) : false); }
template<class T> inline bool chmin(T &a, T const &b) { return (a > b ? (a = b, true) : false); }
// #define DEBUG
#ifdef DEBUG
#include "D:\cpp\debug.h"
#else
#define debug(...)
#define debug_arr(...)
#endif
mt19937 rng((uint32_t)chrono::steady_clock::now().time_since_epoch().count());
constexpr int N = 5E4 + 5, Q = 1E4 + 5;
constexpr int INF = 1E9 + 7;
constexpr ll INFLL = 4E18;
constexpr int MOD = 1E9 + 7; // 998244353
constexpr double EPS = 1E-10;
struct Query {
int a, b, id;
Query(int a, int b, int id): a(a), b(b), id(id) {}
};
vpii adj[N], rev[N];
ll res[Q];
unordered_map<int, unordered_map<int, ll>> d[2];
int k, n, m, q;
void dijkstra(int s, int l, int r, unordered_map<int, ll> &d, vpii adj[]) {
int block_l = l / k, block_r = r / k;
FOR(i, block_l * k, min(n - 1, (block_r + 1) * k - 1)) {
d[i] = INFLL;
}
priority_queue<pll, vpll, greater<pll>> pq;
pq.emplace(0, s);
d[s] = 0;
while (!pq.empty()) {
auto [dist, u] = pq.top();
pq.pop();
if (dist != d[u]) continue;
for (auto &[v, t] : adj[u]) {
if (v / k < block_l || v / k > block_r) continue;
if (chmin(d[v], d[u] + t)) {
pq.emplace(d[v], v);
}
}
}
}
void dnc(int l, int r, vector<Query> &queries) {
if (l / k >= r / k) return;
int m = (l + r) / 2;
int block_m = m / k;
FOR(i, 0, k - 1) {
int x = block_m * k + i;
dijkstra(x, l, m, d[0][x], rev);
dijkstra(x, m, r, d[1][x], adj);
}
vector<Query> todo[2];
for (auto &[l, r, id] : queries) {
if (l <= m && m < r) {
FOR(i, 0, k - 1) {
int x = block_m * k + i;
chmin(res[id], d[0][x][l] + d[1][x][r]);
}
} else {
todo[l > m].emplace_back(l, r, id);
}
}
dnc(l, m, todo[0]);
dnc(m + 1, r, todo[1]);
}
void solve() {
cin >> k >> n >> m >> q;
while (m--) {
int a, b, t;
cin >> a >> b >> t;
// floor(a / k) + 1 = floor(b / k)
adj[a].emplace_back(b, t);
rev[b].emplace_back(a, t);
}
vector<Query> queries;
FOR(i, 1, q) {
int a, b;
cin >> a >> b;
queries.emplace_back(a, b, i);
}
fill(all(res), INFLL);
dnc(0, n - 1, queries);
FOR(i, 1, q) {
cout << (res[i] == INFLL ? -1 : res[i]) << el;
}
}
int main() {
fast_io
#define LOCAL
#ifndef LOCAL
#define PROBLEM ""
freopen(PROBLEM ".INP", "r", stdin);
freopen(PROBLEM ".OUT", "w", stdout);
#endif
int t = 1;
// cin >> t;
while (t--) solve();
}
