#include <bits/stdc++.h>
using namespace std;
#define rep(i, a, b) for (int i = a; i < (b); ++i)
#define per(i, a, b) for (int i = b - 1; i >= (a); --i)
#define trav(a, x) for (auto &a : x)
#define all(x) x.begin(), x.end()
#define sz(x) x.size()
#define pb push_back
#define umap unordered_map
#define uset unordered_set
typedef pair<int, int> ii;
typedef pair<int, ii> iii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<vi> vvi;
typedef long long ll;
const int INF = 1000000007;
int main() {
vii graph[50001];
int n, memo[50001], k, m, o;
scanf("%d %d %d %d", &k, &n, &m, &o);
rep(i, 0, m) {
int u, v, w;
scanf("%d %d %d", &u, &v, &w);
graph[u].emplace_back(v, w);
}
int ans[10000];
iii orders[10000];
rep(i, 0, o) {
orders[i].second.second = i;
scanf("%d %d", &orders[i].first, &orders[i].second.first);
orders[i].second.first *= -1;
}
sort(orders, orders + o);
rep(l, 0, o) {
int a = orders[l].first, b = -orders[l].second.first;
if (!l || a != orders[l - 1].first) {
fill(memo + a, memo + b + 1, INF);
memo[a] = 0;
rep(i, a, b) {
if (INF == memo[i]) continue;
trav(j, graph[i]) {
int v, w;
tie(v, w) = j;
memo[v] = min(memo[v], memo[i] + w);
}
}
}
ans[orders[l].second.second] = memo[b] == INF ? -1 : memo[b];
}
rep(i,0,o)printf("%d\n",ans[i]);
return 0;
}
