#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
template <typename T1, typename T2>
using indexed_map = tree<T1, T2, less<T1>, rb_tree_tag, tree_order_statistics_node_update>;
template <typename T>
using indexed_set = indexed_map<T, null_type>;
#define loop(x, i) for (int i = 0; i < (x); i++)
#define loop1(x, i) for (int i = 1; i <= (x); i++)
#define rev(x, i) for (int i = (int)(x) - 1; i >= 0; i--)
#define itloop(x) for (auto it = begin(x); x != end(x); it++)
#define itrev(x) for (auto it = rbegin(x); x != rend(x); it++)
// #define int long long
// #define INF ((int64_t)(4e18 + 1))
#define INF32 ((int32_t)(2e9 + 1))
#define ALL(x) begin(x), end(x)
#define RALL(x) rbegin(x), rend(x)
#define removeIn(x, l) l.erase(find(ALL(l), x))
#define pb push_back
#define sz(x) (int)(x).size()
#define F first
#define S second
#define var const auto &
#define foreach(l) for (var e : l)
typedef int8_t i8;
typedef int16_t i16;
typedef int32_t i32;
typedef int64_t i64;
typedef pair<int, int> ii;
typedef tuple<int, int, int> iii;
typedef tuple<int, int, int, int> iiii;
typedef vector<int> vi;
typedef vector<i32> vi32;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<vi32> vvi32;
typedef vector<ii> vii;
typedef vector<iii> viii;
typedef vector<vii> vvii;
typedef vector<viii> vviii;
typedef set<int> si;
typedef set<ii> sii;
typedef set<iii> siii;
typedef vector<si> vsi;
typedef vector<sii> vsii;
typedef vector<vsi> vvsi;
typedef vector<string> vstr;
typedef vector<vector<string>> vvstr;
typedef vector<bool> vb;
typedef vector<vb> vvb;
template <typename T1, typename T2>
istream &operator>>(istream &in, pair<T1, T2> &p)
{
    in >> p.first >> p.second;
    return in;
}
template <typename... Args>
ostream &operator<<(ostream &os, const tuple<Args...> &t)
{
    apply([&os](const Args &...args)
          { size_t n = 0;  ((os << ' ' << args), ...); }, t);
    return os;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p)
{
    os << p.F << ' ' << p.S;
    return os;
}
template <typename T>
istream &operator>>(istream &is, vector<T> &vec)
{
    for (auto &element : vec)
        is >> element;
    return is;
}
template <typename T>
ostream &operator<<(ostream &os, vector<T> &vec)
{
    for (auto &element : vec)
        os << element << ' ';
    return os;
}
template <typename... T>
void DBG(T &&...args) { ((cerr << args << ' '), ...) << endl; }
template <typename... T>
void print(T &&...args) { ((cout << args << ' '), ...) << endl; }
template <typename... T>
void read(T &&...args) { ((cin >> args), ...); }
vi nxt(50'000, -1);
vi cost(50'000, 0);
void solve()
{
    int k, n, m, q;
    read(k, n, m, q);
    loop(m, i)
    {
        int a, b, t;
        read(a, b, t);
        nxt.at(a) = b;
        cost.at(a) = b;
    }
    while (q--)
    {
        int a, b;
        read(a, b);
        int res = 0;
        bool done = 0;
        while (nxt.at(a) != -1)
        {
            res += cost.at(a);
            a = nxt.at(a);
            if (a == b)
            {
                done = 1;
                print(res);
                break;
            }
        }
        if (!done)
            print(-1);
    }
}
signed main()
{
    cin.tie(0)->sync_with_stdio(0);
    cin.exceptions(cin.failbit);
    string name = "";
    if (sz(name))
    {
        if (!freopen((name + ".in").c_str(), "r", stdin) || !freopen((name + ".out").c_str(), "w", stdout))
            return 1;
    }
    int t = 1;
    // read(t);
    while (t--)
        solve();
}
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