//Huyduocdithitp
#include <bits/stdc++.h>
typedef long long ll;
#define endl '\n'
#define yes cout<<"YES"<<endl;
#define no cout<<"NO"<<endl;
#define fi first
#define se second
#define pii pair<ll, ll>
#define inf 1e18
#define faster ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define MP make_pair
#define TASK "ghuy4g"
#define start if(fopen(TASK".inp","r")){freopen(TASK".inp","r",stdin);freopen(TASK".out","w",stdout);}
#define LOG 17
#define N 500005
using namespace std;
struct Node {
ll m[5][5];
Node () {
for (int i = 0; i < 5; i ++) {
for (int j = 0; j < 5; j ++) {
m[i][j] = inf;
}
}
}
};
ll k, n, m, o;
Node dp[LOG + 2][50005];
Node combine(Node L, Node R) {
Node res;
for (int i = 0; i < k; i ++) {
for (int j = 0; j < k; j ++) {
for (int l = 0; l < k; l ++) {
if (L.m[i][j] != inf && R.m[j][l] != inf) {
res.m[i][l] = min(res.m[i][l], L.m[i][j] + R.m[j][l]);
}
}
}
}
return res;
}
void prepare() {
for (int j = 1; j <= LOG; j ++) {
for (int i = 0; i <= n / k; i ++) {
dp[j][i] = combine(dp[j - 1][i], dp[j - 1][i + (1 << (j - 1))]);
}
}
}
signed main(void) {
faster;
cin >> k >> n >> m >> o;
for (int i = 1; i <= m; i ++) {
ll u, v, w;
cin >> u >> v >> w;
if (u > v) swap(u, v);
ll x = u % k, y = v % k;
dp[0][u / k].m[x][y] = min(dp[0][u / k].m[x][y], w);
}
prepare();
for (int id = 1; id <= o; id ++) {
ll u, v;
cin >> u >> v; // dp[a][b][x][y]
ll a = u / k, b = v / k, x = u % k, y = v % k;
if (a >= b) {
cout << -1 << endl;
continue;
}
ll dis = b - a;
Node res;
for (int j = 0; j < k; j ++) {
res.m[j][j] = 0;
}
for (int j = LOG; j >= 0; j --) {
if (dis >= (1 << j)) {
dis -= (1 << j);
res = combine(res, dp[j][a]);
a += (1 << j);
}
}
ll kq = res.m[x][y];
if (kq == inf) {
cout << -1 << endl;
continue;
}
cout << kq << endl;
}
return 0;
}
