#include <bits/stdc++.h>
using namespace std;
#define TASK "long"
#define fi first
#define se second
#define ll long long
#define pb push_back
#define ALL(x) (x).begin(), (x).end()
#define GETBIT(mask, i) ((mask) >> (i) & 1)
#define MASK(i) ((1LL) << (i))
#define SZ(x) ((int)(x).size())
#define mp make_pair
#define CNTBIT(mask) __builtin_popcount(mask)
template<class X, class Y> bool maximize(X &x, Y y){ if (x < y) {x = y; return true;} return false;};
template<class X, class Y> bool minimize(X &x, Y y){ if (x > y) {x = y; return true;} return false;};
typedef pair<int, int> ii;
const int N = 1e5 + 5;
const int M = 1e6 + 5;
const int inf = 1e9 + 7;
const long long INF = (long long)1e18 + 7;
const int mod = 1e9 + 7;
struct DSU {
int n;
vector<int> par;
DSU(int _n = 0) {
n = _n;
par.assign(n + 2, -1);
}
int root(int v) {
return par[v] < 0 ? v : (par[v] = root(par[v]));
}
bool join(int x, int y) {
x = root(x);
y = root(y);
if (x == y) return false;
if (par[y] < par[x]) swap(x, y);
par[x] += par[y];
par[y] = x;
return true;
}
} dsu;
struct Edge {
int u, v, c;
Edge(int _u = 0, int _v = 0, int _c = 0) {
u = _u; v = _v; c = _c;
}
} e[M];
vector<ii> adj[N];
int n, K, m, q;
void read() {
cin >> K >> n >> m >> q;
dsu = DSU(n);
for(int i = 1; i <= m; i++) {
int u, v, c; cin >> u >> v >> c;
assert(v - u < 2 * K);
adj[u].push_back({v, c});
dsu.join(u, v);
if (K == 1) assert(v == u + 1);
e[i] = Edge(u, v, c);
}
}
long long dfs(int s, int t) {
vector<long long> d(n + 1, INF);
d[s] = 0;
priority_queue<pair<long long, int>, vector<pair<long long, int>>, greater<pair<long long, int>>> heap;
heap.push({0, s});
while(!heap.empty()) {
auto tmp = heap.top(); heap.pop();
long long du = tmp.fi;
int u = tmp.se;
if (du != d[u]) continue;
if (u == t) break;
for(auto [v, c]: adj[u]) if (minimize(d[v], du + c)) {
heap.push({d[v], v});
}
}
return d[t] == INF ? -1 : d[t];
}
void solve() {
vector<long long> d(n + 2, 0);
if (K == 1) {
for(int i = 1; i <= m; i++) d[e[i].v] = e[i].c;
for(int i = 1; i <= n; i++) d[i] += d[i - 1];
}
vector<long long> d0(n + 1, INF);
d0[0] = 0;
priority_queue<pair<long long, int>, vector<pair<long long, int>>, greater<pair<long long, int>>> heap;
heap.push({0, 0});
while(!heap.empty()) {
auto tmp = heap.top(); heap.pop();
long long du = tmp.fi;
int u = tmp.se;
if (du != d0[u]) continue;
for(auto [v, c]: adj[u]) if (minimize(d0[v], du + c)) {
heap.push({d0[v], v});
}
}
while(q--) {
int u, v; cin >> u >> v;
if (u == v) {
cout << 0 << endl;
continue;
}
if (u > v || u/K == v/K || dsu.root(u) != dsu.root(v)) {
cout << -1 << endl;
continue;
}
if (K == 1) {
cout << d[v] - d[u] << endl;
continue;
}
if (u == 0) {
cout << (d0[v] == INF ? -1 : d0[v]) << endl;
continue;
}
cout << dfs(u, v) << endl;
}
}
signed main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
if (fopen(TASK".inp", "r")) {
freopen(TASK".inp", "r", stdin);
freopen(TASK".out", "w", stdout);
}
int test = 1;
// cin >> test;
while(test--) {
read();
solve();
}
return 0;
}
// rmq - rmq2d
// hash
// fw - fw2d
// segtree
