#include <iostream>
#include <bits/stdc++.h>
using namespace std;
long long k;vector<pair<int,int>> adj[100001],rev[1000001];
long long an[100001];
map<pair<int,int>,long long> mp;
void dc(int l,int r,vector<pair<pair<int,int>,int>> qu){
if(l>=r)return;
int md = (l+r)/2;
long long ll[k][(int)k*(md-l+1)],rr[k][(k*(r-md))];
for(int j = md;j>=l;j--){
for(int z = 0;z<k;z++){
for(int a = 0;a<k;a++){
if(j==md){
if(z==a){
ll[a][((md+1)*k-1)-(j*k+z)] = 0;
}
else ll[a][((md+1)*k-1)-(j*k+z)] = 1e9;
continue;
}
ll[a][((md+1)*k-1)-(j*k+z)] = 1e9;
for(auto e:adj[j*k+z]){
ll[a][((md+1)*k-1)-(j*k+z)] = min(ll[a][((md+1)*k-1)-(j*k+z)],ll[a][((md+1)*k-1)-e.first]+e.second);
}
}
}
}
for(int j = md+1;j<=r;j++){
for(int z = 0;z<k;z++){
for(int a = 0;a<k;a++){
if(j==md+1){
if(z==a)rr[a][(j*k+z)-((md+1)*k)] = 0;
else rr[a][(j*k+z)-((md+1)*k)] = 1e9;
continue;
}
rr[a][(j*k+z)-((md+1)*k)] = 1e9;
for(auto e:rev[j*k+z]){
rr[a][(j*k+z)-((md+1)*k)] = min(rr[a][(j*k+z)-((md+1)*k)],rr[a][e.first-((md+1)*k)]+e.second);
}
}
}
}
vector<pair<pair<int,int>,int>> R,L;
for(auto i:qu){
if(i.first.first/k>md){
R.push_back(i);
}else if(i.first.second/k<md){
L.push_back(i);
}else{
if((i.first.second/k)==md){
an[i.second] = ll[i.first.second%k][((md+1)*k-1)-i.first.first];
}else{
long long ans = 1e18;
for(int z = 0;z<k;z++){
for(int e = 0;e<k;e++){
ans = min(ans,ll[z][((md+1)*k-1)-i.first.first]+rr[e][i.first.second-((md+1)*k)]+(mp.count(make_pair((md*k)+z,(md+1)*k+e))==0?1000000000:mp[{(md*k)+z,(md+1)*k+e}]));
}
}
an[i.second] = ans;
}
}
}
dc(l,md-1,L);dc(md+1,r,R);
}
int main(){
memset(an,-1,sizeof an);
int n,m,o;
cin>>k>>n>>m>>o;
for(int i = 0;i<m;i++){
long long a,b,c;
cin>>a>>b>>c;
mp[{a,b}] = c;
adj[a].push_back({b,c});
rev[b].push_back({a,c});
}
vector<pair<pair<int,int>,int>> qu;
for(int i = 0;i<o;i++){
long long a,b;cin>>a>>b;
if(a==b){
an[i] = 0;continue;
}
qu.push_back({{a,b},i});
}
dc(0,(n-1)/k,qu);
for(int i = 0;i<o;i++){
cout<<(an[i]>=1e9?-1:an[i])<<endl;
}
return 0;
}
