#include <bits/stdc++.h>
using namespace std;
#define name "optcost"
#define MAXN 50004
#define pb push_back
#define pf push_front
#define ll long long
#define ii pair<int, int>
#define fs first
#define sc second
#define ill pair<int, ll>
#define lli pair<ll, int>
#define llll pair<ll, ll>
#define all(v) v.begin(),v.end()
#define uni(v) v.erase(unique(all(v)),v.end())
#define bit(n,i) (((n)>>(i))&1)
#define FOR(i,a,b) for (int i=(a),_b=(b); i<=_b; i++)
#define FORD(i,a,b) for (int i=(a),_b=(b); i>=_b; i--)
#define MASK(i) (1LL<<(i))
const int INF=1e9;
const int MOD=1e9+7;
void add(int &u, int v){
u+=v;
if (u>=MOD) u-=MOD;
}
void sub(int &u, int v){
u-=v;
if (u<0) u+=MOD;
}
void minimize(int &u, int v){
u=min(u,v);
}
void maximize(int &u, int v){
u=max(u,v);
}
long long Rand(long long l, long long r){
ll tmp=0;
FOR(i,1,4) tmp=((tmp<<15)^(((1<<15)-1)&rand()));
return l+tmp%(r-l+1);
}
int k,n,m,q;
struct Edge{
int x,y,w;
}e[MAXN];
ii query[(int)1e4+7];
map<ii,int> mp;
const int LOG=15;
int spa[MAXN][LOG+1][5][5];
int dp[MAXN],f[MAXN];
int group[MAXN];
vector<int> vec[MAXN];
int main()
{
ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
cin>>k>>n>>m>>q;
FOR(i,1,m) cin>>e[i].x>>e[i].y>>e[i].w;
FOR(i,1,q) cin>>query[i].fs>>query[i].sc;
FOR(i,1,m){
++e[i].x;
++e[i].y;
}
FOR(i,1,q){
++query[i].fs;
++query[i].sc;
}
FOR(i,1,m){
mp[(ii){e[i].x,e[i].y}]=e[i].w;
}
FOR(i,1,n) group[i]=(i%k==0?(int)i/k:(int)i/k+1);
FOR(i,1,n) vec[group[i]].pb(i);
memset(spa,0x3f,sizeof(spa));
FOR(layer,1,group[n]-1){
for (int i:vec[layer]){
int x=i%k;
for (int j:vec[layer+1]){
int y=j%k;
if (mp.find((ii){i,j})!=mp.end()) spa[layer][0][x][y]=mp[(ii){i,j}];
}
}
}
FOR(w,1,LOG){
FOR(layer,1,group[n]-MASK(w)){
for (int i:vec[layer]){
int x=i%k;
for (int j:vec[layer+MASK(w)]){
int y=j%k;
for (int u:vec[layer+MASK(w-1)]){
int z=u%k;
minimize(spa[layer][w][x][y],spa[layer][w-1][x][z]+spa[layer+MASK(w-1)][w-1][z][y]);
}
}
}
}
}
FOR(id,1,q){
int u=query[id].fs,v=query[id].sc;
if (group[u]>=group[v]){
if (u==v) cout<<0<<"\n";
else cout<<-1<<"\n";
continue;
}
FOR(i,0,k-1) dp[i]=spa[0][0][0][0];
dp[u%k]=0;
int cur=group[u];
FORD(w,LOG,0){
if (cur+MASK(w)<=group[v]){
FOR(j,0,4) f[j]=spa[0][0][0][0];
FOR(i,0,4){
FOR(j,0,4){
minimize(f[j],dp[i]+spa[cur][w][i][j]);
}
}
FOR(i,0,4) dp[i]=f[i];
cur+=MASK(w);
}
}
cout<<(dp[v%k]>INF?-1:dp[v%k])<<"\n";
}
return 0;
}
