#include <bits/stdc++.h>
using namespace std;
template<typename T, class F = function<T(const T&, const T&)>>
class SparseTable {
public:
int n;
vector<vector<T>> mat;
F func;
SparseTable(const vector<int>& a, const F& f) : func(f) {
n = (int) a.size();
mat.resize(n);
int max_log = 32 - __builtin_clz(n);
mat[0] = a;
for (int j = 1; j < max_log; j++) {
mat[j].resize(n - (1 << j) + 1);
for (int i = 0; i <= (n - (1 << j)); i++) {
mat[j][i] = func(mat[j - 1][i], mat[j - 1][i + (1 << (j - 1))]);
}
}
}
T get(int from, int to) {
assert(from <= to && from >= 0 && to <= n - 1);
int lg = 32 - __builtin_clz(to - from + 1) - 1;
return func(mat[lg][from], mat[lg][to - (1 << lg) + 1]);
}
};
const int N = 50000;
const int inf = 1000000000;
int dp[N];
bool inQue[N];
vector<array<int, 2>> adj[N];
vector<array<int, 2>> rAdj[N];
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
int k, n, m, q;
cin >> k >> n >> m >> q;
int p = (n + k - 1) / k;
vector<vector<int>> bucket(p);
for (int i = 0; i < n; i++) {
bucket[i / k].push_back(i);
}
for (int i = 0; i < n; i++) {
inQue[i] = false;
dp[i] = inf;
}
for (int i = 0; i < m; i++) {
int u, v, t;
cin >> u >> v >> t;
adj[u].push_back({v, t});
rAdj[v].push_back({u, t});
}
vector<vector<vector<vector<pair<int, int>>>>> pts(p * 2, vector<vector<vector<pair<int, int>>>> (k, vector<vector<pair<int, int>>> (2)));
auto Solve = [&](int midPoint, int cnt) {
for (int each = 0; each < (int) bucket[midPoint].size(); each++) {
int x = bucket[midPoint][each];
dp[x] = 0;
pts[cnt][each][0].emplace_back(x, 0);
pts[cnt][each][1].emplace_back(x, 0);
for (int it = x - 1; it >= 0; it--) {
if (inQue[it / k]) {
break;
}
for (auto y : adj[it]) {
dp[it] = min(dp[it], dp[y[0]] + y[1]);
}
pts[cnt][each][0].emplace_back(it, dp[it]);
}
reverse(pts[cnt][each][0].begin(), pts[cnt][each][0].end());
for (int it = x - 1; it >= 0; it--) {
if (inQue[it / k]) {
break;
}
dp[it] = inf;
}
for (int it = x + 1; it < n; it++) {
if (inQue[it / k]) {
break;
}
for (auto y : rAdj[it]) {
dp[it] = min(dp[it], dp[y[0]] + y[1]);
}
pts[cnt][each][1].emplace_back(it, dp[it]);
}
for (int it = x; it < n; it++) {
if (inQue[it / k]) {
break;
}
dp[it] = inf;
}
}
};
vector<int> at(p, inf);
auto Divide = [&]() {
int cnt = 0;
queue<array<int, 2>> que;
que.push({0, p - 1});
while (!que.empty()) {
auto t = que.front();
que.pop();
int low = t[0];
int high = t[1];
if (low >= high) {
continue;
}
int midPoint = low + (high - low) / 2;
Solve(midPoint, cnt);
inQue[midPoint] = true;
at[midPoint] = cnt;
cnt++;
que.push({low, midPoint});
que.push({midPoint + 1, high});
}
};
Divide();
SparseTable<int> st(at, [&](int i, int j) {
return min(i, j);
});
while (q--) {
int u, v;
cin >> u >> v;
int b0 = u / k;
int b1 = v / k;
if (b0 == b1) {
cout << -1 << '\n';
} else {
int ans = inf;
int cnt = st.get(b0, b1);
for (int each = 0; each < k; each++) {
if (pts[cnt][each][0].empty()) {
break;
}
int it0 = lower_bound(pts[cnt][each][0].begin(), pts[cnt][each][0].end(), make_pair(u, -inf)) - pts[cnt][each][0].begin();
int it1 = lower_bound(pts[cnt][each][1].begin(), pts[cnt][each][1].end(), make_pair(v, -inf)) - pts[cnt][each][1].begin();
if (it0 < (int) pts[cnt][each][0].size() && it1 < (int) pts[cnt][each][1].size()) {
if (pts[cnt][each][0][it0].first == u && pts[cnt][each][1][it1].first == v) {
ans = min(ans, pts[cnt][each][0][it0].second + pts[cnt][each][1][it1].second);
}
}
}
if (ans < inf) {
cout << ans << '\n';
} else {
cout << -1 << '\n';
}
}
}
return 0;
}
