#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define int long long
const int MOD = 1e9 + 7;
const int INF = 1e15;
const int N = 1e6;
int n, m, k, a, b, c, d, h, l, r, p, q, u, v, x, y;
vector<int> arr(N);
vector<int> adj[N];
vector<int> vis(N);
vector<int> depths(N);
map<pair<int, int>, int> weight;
vector<int> id(N);
vector<int> indeg(N, -1);
vector<int> component;
void dfs(int node, int dist) {
vis[node] = true;
component.pb(node);
if(dist > x) {
x = dist;
y = node;
}
// cout << node << " ";
for(auto j : adj[node]) {
if(!vis[j]) {
dfs(j, dist+weight[{node, j}]);
}
}
}
void line() {
l = 1;
for(int i = 0; i<n; i++) {
if(!vis[i] && indeg[i]==-1) {
x = 0;
y = i;
component.clear();
dfs(i, 0);
for(auto j : component) {
id[j] = l;
// cout << j << " ";
}
// cout << "\n";
h = 0;
while(indeg[y]!=-1) {
h += weight[{y, indeg[y]}];
y = indeg[y];
depths[y] = h;
}
l++;
}
}
// for(int i = 0; i<n; i++) cout << depths[i] << " ";
// cout << "\n";
while(q--) {
cin >> a >> b;
// cout << id[a] << " " << id[b] << " ";
if(id[a] != id[b] || depths[a] < depths[b]) {
cout << -1 << "\n";
continue;
}
else {
cout << depths[a]-depths[b] << "\n";
}
}
}
void solve() {
cin >> k >> n >> m >> q;
bool sub2 = true;
for(int i = 1; i<=m; i++) {
cin >> a >> b >> c;
if(a!=0) {
sub2 = false;
}
adj[a].pb(b);
weight[{a, b}] = c;
weight[{b, a}] = c;
indeg[b] = a;
}
if(k==1) {
line();
return;
}
if(sub2) {
while(q--) {
cin >> a >> b;
if(indeg[b]!=-1) {
cout << weight[{a, b}];
}
else cout << -1;
cout << '\n';
}
}
}
int32_t main() {
ios::sync_with_stdio(false);
cout.tie(0); cin.tie(0);
int tc = 1;
while(tc--) {
solve();
}
return 0;
}
