#include <bits/stdc++.h>
#define MAXN 50001
#define INF 100000000000000
#define ii pair<int, int>
#define iii pair<ii, int>
#define ll long long
using namespace std;
ll dist[MAXN][5][5];
ll ans[MAXN];
int K, N, M, O;
ll weights[5][5][MAXN];
void dnc(int l, int r, vector<iii> q){
if( l == r ){
for( auto x : q ) ans[x.second] = -1;
return;
}
int m = (l+r)/2;
for( int i{0} ; i < K ; ++i ) for( int j{0} ; j < K ; ++j ){
if( i == j ) dist[m][i][j] = 0;//, dist[m+1][i][j] = 0;
else dist[m][i][j] = INF;//, dist[m+1][i][j] = INF;
}
for( int lev{m-1} ; lev >= l ; --lev ){
for( int i{0} ; i < K ; ++i ) for( int k{0} ; k < K ; ++k ){
dist[lev][i][k] = INF;
for( int j{0} ; j < K ; ++j ){
dist[lev][i][k] = min(dist[lev+1][j][k]+weights[i][j][lev], dist[lev][i][k]);
}
}
}
for( int lev{m+1} ; lev <= r ; ++lev ){
for( int i{0} ; i < K ; ++i ) for( int k{0} ; k < K ; ++k ){
dist[lev][i][k] = INF;
for( int j{0} ; j < K ; ++j ){
dist[lev][i][k] = min(dist[lev-1][i][j]+weights[j][k][lev-1], dist[lev][i][k]);
}
}
}
vector<iii> lft, rght;
for( auto x : q ){
int a = x.first.first, b = x.first.second;
int id = x.second;
int l1 = a/K, l2 = b/K;
a %= K; b %= K;
if( l1 <= m && l2 >= m ){
ans[id] = INF;
for( int c{0} ; c < K ; ++c ) ans[id] = min(ans[id], dist[l1][a][c]+dist[l2][c][b]);
}
else if( l2 <= m ) lft.push_back(x);
else rght.push_back(x);
}
dnc(l, m, lft);
dnc(m+1, r, rght);
}
int main(){
cin>>K>>N>>M>>O;
for( int i{0} ; i < K ; ++i ) for( int j{0} ; j < K ; ++j ) for( int k{0} ; k < (N-1)/K ; ++k ) weights[i][j][k] = INF;
for( int i{1} ; i <= M ; ++i ){ //multi edges??
int u, v, w;
cin>>u>>v>>w;
int lev = u/K;
u %= K; v %= K;
weights[u][v][lev] = w;
}
vector<iii> queries;
for( int i{1} ; i <= O ; ++i ){
int u, v;
cin>>u>>v;
queries.push_back(iii(ii(u, v), i));
}
dnc(0, (N-1)/K, queries);
for( int i{1} ; i <= O ; ++i ){
if( ans[i] < INF ) cout<<ans[i]<<'\n';
else cout<<"-1\n";
}
return 0;
}
