#include <bits/stdc++.h>
using namespace std;
#define MAXN 50005
#define BLOCK 500
#define INF 10000000000000000ll
int len, n, m, q;
vector<pair<int, int>> adj[MAXN];
vector<pair<int, int>> revadj[MAXN];
long long dist[MAXN/BLOCK+10][MAXN/BLOCK+10][5][5];
long long bfs(int a, int b){
if(a >= n || b >= n) return INF;
if(b/len <= a/len) return INF;
long long dp[5*BLOCK+100];
fill(dp, dp+5*BLOCK+100, INF);
dp[0] = 0;
queue<int> q;
q.push(a);
while(!q.empty() && q.front() < b){
int v = q.front();
// cout << v << endl;
q.pop();
if(dp[v-a] == INF) continue;
for(auto u : adj[v]){
if(dp[u.first-a] == INF){
// cout << u.first << endl;
q.push(u.first);
}
// cout << u.first << endl;
dp[u.first-a] = min(dp[u.first-a], dp[v-a]+u.second);
}
}
return dp[b-a];
}
int main(){
// freopen("a.in", "r", stdin);
ios_base::sync_with_stdio(false);
cin.tie(0);
cin >> len >> n >> m >> q;
for(int i = 0; i<m; i++){
int a, b, w; cin >> a >> b >> w;
adj[a].push_back({b, w});
revadj[b].push_back({a, w});
}
for(int i = ((n-1)/len/BLOCK)*BLOCK; i>=0; i -= BLOCK){
for(int a = 0; a<len; a++){
for(int b = 0; b<len; b++){
dist[i/BLOCK][i/BLOCK][a][b] = INF;
if(a == b) dist[i/BLOCK][i/BLOCK][a][b] = 0;
}
for(int j = i+BLOCK; j<=(n-1)/len; j+=BLOCK){
for(int b = 0; b<len; b++){
if(j == i+BLOCK){
dist[i/BLOCK][j/BLOCK][a][b] = bfs(i*len+a, j*len+b);
continue;
}
dist[i/BLOCK][j/BLOCK][a][b] = INF;
for(int c = 0; c<len; c++){
dist[i/BLOCK][j/BLOCK][a][b] = min(dist[i/BLOCK][j/BLOCK][a][b], dist[i/BLOCK][j/BLOCK-1][a][c]+dist[j/BLOCK-1][j/BLOCK][c][b]);
}
}
}
}
}
// cout << ceil((BLOCK+1.0)/BLOCK) << endl;
while(q--){
int a, b; cin >> a >> b;
int ca = a%len, cb = b%len;
int la = a/len, lb = b/len;
if(lb <= la){
cout << -1 << endl;
continue;
}
if(la/BLOCK == lb/BLOCK){
long long ans = bfs(a, b);
if(ans == INF) cout << -1 << endl;
else cout << ans << endl;
continue;
}
// cout << "hi" << endl;
int na = ceil((la+0.0)/BLOCK)*BLOCK;
int pb = lb/BLOCK*BLOCK;
long long dp[5*BLOCK+100];
fill(dp, dp+5*BLOCK+100, INF);
dp[0] = 0;
queue<int> q;
q.push(a);
while(!q.empty() && q.front() < na*len+len){
int v = q.front();
q.pop();
if(dp[v-a] == INF) continue;
for(auto u : adj[v]){
if(dp[u.first-a] == INF) q.push(u.first);
dp[u.first-a] = min(dp[u.first-a], dp[v-a]+u.second);
}
}
long long revdp[5*BLOCK+100];
fill(revdp, revdp+5*BLOCK+100, INF);
revdp[0] = 0;
queue<int> revq;
revq.push(b);
while(!revq.empty() && revq.front() > pb*len-1){
int v = revq.front();
revq.pop();
if(revdp[b-v] == INF) continue;
for(auto u : revadj[v]){
if(revdp[b-u.first] == INF) revq.push(u.first);
revdp[b-u.first] = min(revdp[b-u.first], revdp[b-v]+u.second);
}
}
long long ans = INF;
for(int i = 0; i<len; i++){
for(int j = 0; j<len; j++){
long long v1, v2;
if(na*len+i-a < 0) v1 = INF;
else v1 = dp[na*len+i-a];
if(b-(pb*len+j) < 0) v2 = INF;
else v2 = revdp[b-(pb*len+j)];
ans = min(ans, v1+dist[na/BLOCK][pb/BLOCK][i][j]+v2);
}
}
if(ans == INF) cout << -1 << endl;
else cout << ans << endl;
}
}
