//!!in the name of god!!
#include<bits/stdc++.h>
#define space <<' '<<
#define endl '\n'
#define inf 1e9
#define F first
#define S second
#define PB push_back
#define PF push_front
#define pll pair<ll,ll>
#define pii pair<int,int>
#define md(a) ((a+mod)%mod)
#define MP(a,b) make_pair(a,b)
#define all(a) a.begin(),a.end()
#define MT(a,b,c) make_tuple(a,b,c)
#define has(a,b) (a.find(b)!=a.end())
typedef long long ll;
using namespace std;
template<typename t> using heap=
priority_queue<t,vector<t>,greater<t>>;
const int mx = 5e4+5;
const int lg = 32;
map<int,ll> adj[mx][lg];
int glg(int v){
if(v<2)return 0;
return glg(v/2)+1;
}
int main(){
std::ios::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
int k,n,m,o;
cin>>k>>n>>m>>o;
for(int u,v,t;m--;)
cin>>u>>v>>t,
adj[u][0][v]=t;
for(int t=0;t<n;t++)
for(int p=1;p<lg;p++){
for(auto e:adj[t][p-1])
for(auto d:adj[e.F][p-1])
if(has(adj[t][p],d.F))
adj[t][p][d.F]=min(adj[t][p][d.F],e.S+d.S);
else
adj[t][p][d.F]=e.S+d.S;
}
map<int,ll> cn,te;
for(int a,b;o--;){
cin>>a>>b;
int c=a/k,t=b/k;
cn.clear();
cn[a]=0;
while(c<t){
te.clear();
int ne=glg(c-t);
for(auto e:cn)
for(auto d:adj[e.F][ne])
if(has(te,d.F))
te[d.F]=min(te[d.F],e.S+d.S);
else te[d.F]=e.S+d.S;
cn=te;
c+=1<<ne;
}
if(has(cn,b)) cout<<cn[b]<<endl;
else cout<<-1<<endl;
}
return 0;
}
