#include <bits/stdc++.h>
#define all(v) v.begin(), v.end()
#define sz(x) (int)x.size()
#define pb push_back
#define pii pair<int, int>
#define chmin(x, v) x = min(x, v)
#define chmax(x, v) x = max(x, v)
#define print(x) cout << #x << " est " << x << endl;
#define x first
#define y second
#define int long long
using namespace std;
const int K = 5, N = 1e5, OO = 1e9, B = 17;
struct Chemin {
int dMin[K][K];
void init(int a){
for (int i = 0; i < K; ++i)
for (int j = 0; j < K; ++j)
dMin[i][j] = a;
}
void combine(Chemin left, Chemin right){
for (int i = 0; i < K; ++i)
for (int j = 0; j < K; ++j){
dMin[i][j] = OO;
for (int k = 0; k < K; ++k)
chmin(dMin[i][j], left.dMin[i][k] + right.dMin[k][j]);
}
}
};
Chemin chemins[N][B];
signed main(){
int tZone, nNoeuds, nAretes, nReqs; cin >> tZone >> nNoeuds >> nAretes >> nReqs;
int nZones = ceil(nNoeuds/double(tZone));
for (int iZone = 0; iZone < nZones; ++iZone)
chemins[iZone][0].init(OO);
for (int i = 0; i < nAretes; ++i){
int source, destination, poids; cin >> source >> destination >> poids;
swap(source, destination);
int zoneSource = source/tZone;
chmin(chemins[zoneSource][0].dMin[source%tZone][destination%tZone], poids);
// cout << "c " << chemins[zoneSource][0].dMin[source%tZone][destination%tZone] << endl;
}
int pow2 = 2;
for (int b = 1; b < B; ++b, pow2 *= 2){
for (int source = nZones - 1; source - pow2 >= 0; --source)
chemins[source][b].combine(chemins[source][b - 1], chemins[source - pow2/2][b - 1]);
}
for (int iReq = 0; iReq < nReqs; ++iReq){
int source, dest; cin >> source >> dest;
swap(source, dest);
int zoneSource = source/tZone, zoneDest = dest/tZone;
Chemin cCur; cCur.init(OO);
for (int i = 0; i < K; ++i)
cCur.dMin[i][i] = 0;
// cout << zoneSource << " " << zoneDest << endl;
int pow2 = 1;
for (int i = 0; i < B - 1; ++i)
pow2 *= 2;
for (int b = B - 1; b >= 0; --b, pow2 /= 2){
// cout << zoneSource << " " << zoneDest << endl;
if (zoneSource - pow2 >= zoneDest){
// if (false)
// cout << "req " << iReq << endl;
// cout << "req " << iReq << " " << b << endl;
cCur.combine(cCur, chemins[zoneSource][b]);
zoneSource -= pow2;
}
}
if (cCur.dMin[source%tZone][dest%tZone] < OO)
cout << cCur.dMin[source%tZone][dest%tZone] << endl;
else
cout << -1 << endl;
}
return 0;
}
