#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ull unsigned long long
#define ld long double
#define pii pair<int, int>
#define fi first
#define se second
#define __builtin_popcount __builtin_popcountll
#define all(x) (x).begin(), (x).end()
#define BIT(x, i) (((x) >> (i)) & 1)
#define MASK(x) ((1ll << (x)))
#define debug(a, l, r) for (int _i = (l); _i <= (r); ++_i) cout << (a)[_i] << ' '; cout << '\n';
const int MAXN = 5e4 + 5;
const int INF = 1e18 + 7;
int k, n, m, q, dp[MAXN];
vector<pii> adj[MAXN];
void init() {
cin >> k >> n >> m >> q;
for (int i = 1; i <= m; ++i) {
int u, v, w; cin >> u >> v >> w;
adj[u].push_back({v, w});
}
}
void solve() {
while (q--) {
int u, v; cin >> u >> v;
for (int i = u; i <= v; ++i) dp[i] = INF;
dp[u] = 0;
for (int i = u; i <= v; ++i) {
for (auto &e : adj[i]) {
dp[e.fi] = min(dp[e.fi], dp[i] + e.se);
}
}
cout << (dp[v] == INF ? -1 : dp[v]) << '\n';
}
}
signed main() {
#ifdef NCTHANH
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
ios_base::sync_with_stdio(0);
cin.tie(nullptr); cout.tie(nullptr);
init();
solve();
return 0;
}
