/*
بسم الله الرحمن الرحيم
Author:
(:Muhammad Aneeq:)
*/
#include <iostream>
#include <vector>
#include <queue>
#include <map>
using namespace std;
map<pair<int,int>,int>d;
int const N=5e4+10;
vector<pair<int,int>>nei[N]={};
int dist[N]={};
bool vis[N]={};
int bfs(int n,int tar)
{
priority_queue<pair<int,int>,vector<pair<int,int>>,greater<pair<int,int>>>pq;
pq.push({0,n});
dist[n]=0;
while (pq.size())
{
int z=pq.top().second;
pq.pop();
if (vis[z])
continue;
if (z==tar)
return dist[z];
vis[z]=1;
for (auto [j,w]:nei[z])
{
if (dist[j]>dist[z]+w)
{
dist[j]=dist[z]+w;
pq.push({dist[j],j});
}
}
}
return -1;
}
inline void solve()
{
int n,m,k,o;
cin>>k>>n>>m>>o;
while (m--)
{
int a,b,t;
cin>>a>>b>>t;
nei[a].push_back({b,t});
}
vector<pair<int,int>>ord;
bool w=1;
while (o--)
{
int x,y;
cin>>x>>y;
w=(w&&(x==0));
ord.push_back({x,y});
}
if (w)
{
for (int i=0;i<n;i++)
dist[i]=1e9+10,vis[i]=0;
bfs(0,-1);
for (auto i:ord)
cout<<(dist[i.second]==1e9+10?-1:dist[i.second])<<'\n';
}
else if (k==1)
{
for (int i=0;i<n;i++)
dist[i]=1e9+10,vis[i]=0;
bfs(0,-1);
for (auto i:ord)
{
if (dist[i.first]==1e9+10||dist[i.second]==1e9+10)
cout<<-1<<endl;
else
cout<<dist[i.second]-dist[i.first]<<endl;
}
}
else
{
for (auto i:ord)
{
for (int j=0;j<n;j++)
dist[j]=1e9+10,vis[j]=0;
cout<<bfs(i.first,i.second)<<'\n';
}
}
}
int main()
{
ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
solve();
}
