#include<bits/stdc++.h>
using namespace std;
#define int long long
#define maxn 50050
#define f first
#define s second
int32_t main(){
ios::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
int k,no_of_vertex,no_of_edge,no_of_query;
int input1,input2,input3;
cin >> k >> no_of_vertex >> no_of_edge >> no_of_query;
vector<vector<pair<int,int> > > adj(maxn);
for(int i=0;i<no_of_edge;i++){
cin >> input1 >> input2 >> input3;
adj[input1].push_back({input2,input3});
}
vector<int> dist(maxn,INT_MAX);
priority_queue<pair<int,int>,vector<pair<int,int> >,greater<pair<int,int> > > q1;
dist[0] = 0;
q1.push({0,0});
while(q1.size()!=0){
pair<int,int> a = q1.top();
q1.pop();
for(auto j:adj[a.s]){
if(dist[j.f]>a.f+j.s){
dist[j.f] = a.f+j.s;
q1.push({dist[j.f],j.f});
}
}
}
for(int i=0;i<no_of_query;i++){
cin >> input1 >> input2;
if(dist[input2]==INT_MAX){
cout << -1 << "\n";
}
else{
cout << dist[input2] << "\n";
}
}
}
