#pragma GCC optimize("Ofast,unroll-loops")
// #pragma comment(linker, "/stack:200000000")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,fma,tune=native")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
typedef int ll;
typedef long double ld;
typedef pair <ll, ll> pll;
#ifdef SINA
#define dbg(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1> void __f(const char* name, Arg1&& arg1) { cout << name << " : " << arg1 << std::endl; }
template <typename Arg1, typename... Args> void __f (const char* names, Arg1&& arg1, Args&&... args) {
const char* comma = strchr(names + 1, ',');cout.write(names, comma - names) << " : " << arg1<<" | ";__f(comma+1, args...); }
#define dbg2(x, j, n) cout<< #x << " : "; output((j), (n), x, 1); cout.flush();
#else
#define dbg(...) 0
#define dbg2(x, j, n) 0
#endif
#define SZ(x) ((ll)((x).size()))
#define File(s, t) freopen(s ".txt", "r", stdin); freopen(t ".txt", "w", stdout);
#define input(j, n, a) for (int _i = (j); _i < (n)+(j); _i++) cin>> a[_i];
#define output(j, n, a, t) for (int _i = (j); _i < (n)+(j); _i++) cout<< a[_i] << (((t) && _i != (n)+(j)-1)? ' ' : '\n');
#define kill(x) return cout<< (x) << endl, 0
#define cl const ll
#define fr first
#define sc second
#define lc (v << 1)
#define rc (lc | 1)
#define mid ((l + r) >> 1)
#define All(x) (x).begin(), (x).end()
cl inf = sizeof(ll) == 4 ? (1e9 + 10) : (3e18), mod = 1e9 + 7, MOD = 998244353;
template <class A,class B> ostream& operator << (ostream& out,const pair<A,B>&a){return out<<'('<<a.first<<", "<<a.second<<')';}
template <class A> ostream& operator << (ostream& out, const vector<A> &a) {
out<< '['; for (int i = -1; ++i < int(a.size());) out<< a[i] << (i + 1 < int(a.size()) ? ", " : ""); return out<<']'; }
template <class T, typename _t = less <T> > using Tree = tree <T, null_type, _t, rb_tree_tag, tree_order_statistics_node_update>;
cl N = 5e4 + 3, K = 5, SQ = 230;
ll dis [N][SQ], dist [2][K], t, pos [N], k, n, m, q, ans;
vector <ll> lev [N], vec;
vector <array <ll, 2>> adj [N];
void build (ll L, ll en) {
ll x = en / k;
memset(dist[t], 63, sizeof dist[t]);
dist[t][en % k] = 0;
for (t ^= 1, x--; L <= x; x--, t ^= 1) {
memset(dist[t], 63, sizeof dist[t]);
for (auto &v : lev[x]) for (auto &u : adj[v]) dist[t][v % k] = min(dist[t][v % k], dist[1 - t][u[0] % k] + u[1]);
}
t ^= 1;
}
int main ()
{
ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
memset(dis, 63, sizeof dis);
memset(pos, -1, sizeof pos);
cin>> k >> n >> m >> q;
for (ll i = 0; i < n; i++) {
lev[i / k].push_back(i);
if (!((i / k) % SQ)) pos[i] = SZ(vec), vec.push_back(i);
}
for (ll i = 0, v, u, w; i < m; i++) {
cin>> v >> u >> w;
adj[v].push_back({u, w});
}
for (ll r = (n - 1) / k; ~r; r--) for (auto v : lev[r]) {
if (~pos[v]) dis[v][pos[v]] = 0;
for (auto &u : adj[v]) for (ll i = 0; i < SZ(vec); i++) dis[v][i] = min(dis[v][i], dis[u[0]][i] + u[1]);
}
for (ll v, u, x; q--;) {
cin>> v >> u;
if ((v / k) >= (u / k)) { cout<< -1 << '\n'; continue; }
x = ((u / k) / SQ) * SQ;
if (x < (v / k)) {
build(v / k, u);
if (dist[t][v % k] >= inf) cout<< -1 << '\n';
else cout<< dist[t][v % k] << '\n';
} else {
ans = inf;
build(x, u);
for (auto &p : lev[x]) ans = min(ans, dis[v][pos[p]] + dist[t][p % k]);
if (ans >= inf) ans = -1;
cout<< ans << '\n';
}
}
cerr<< "\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\n";
return 0;
}
/*
5 14 5 5
0 5 9
5 12 10
0 7 7
7 12 8
4 7 10
0 12
0 5
0 7
7 12
0 13
*/
