#include <bits/stdc++.h>

using namespace std;
using ll = long long;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, ma, mb;
    ll k;
    cin >> n >> ma >> mb >> k;

    vector<int> fa1(n), fa2(n), sz1(n), sz2(n);
    vector<vector<int>> sub1(n), sub2(n);
    vector<map<int, int>> cnt(n);
    ll ans = 0;

    function<int(int)> find1 = [&](int x) {
        return x == fa1[x] ? x : find1(fa1[x]);
    };
    function<int(int)> find2 = [&](int x) {
        return x == fa2[x] ? x : find2(fa2[x]);
    };

    iota(fa1.begin(), fa1.end(), 0), iota(fa2.begin(), fa2.end(), 0);
    fill(sz1.begin(), sz1.end(), 1), fill(sz2.begin(), sz2.end(), 1);

    for (int i = 0; i < n; ++i) {
        sub1[i] = sub2[i] = {i};
        cnt[i][i] += 1;
    }

    vector<array<int, 3>> ea(ma), eb(mb);

    for (int i = 0; i < ma; ++i) {
        int u, v, w;
        cin >> u >> v >> w;
        ea[i] = {w, u - 1, v - 1};
    }
    for (int i = 0; i < mb; ++i) {
        int u, v, w;
        cin >> u >> v >> w;
        eb[i] = {w, u - 1, v - 1};
    }

    sort(ea.begin(), ea.end()), sort(eb.begin(), eb.end());

    vector<int> stkSz;
    vector<pair<int, int>> stk;

    auto f = [&](int &x, int d) {
        ans += 1LL * x * (x - 1) / 2;
        x += d;
        ans -= 1LL * x * (x - 1) / 2;
    };

    for (auto [w, a, b] : eb) {
        a = find2(a), b = find2(b);
        stkSz.push_back(stk.size());
        if (a == b) {
            continue;
        }
        if (sz2[a] < sz2[b]) {
            swap(a, b);
        }
        ans += 1LL * sz2[a] * sz2[b];
        stk.push_back({a, b});
        fa2[b] = a;
        sz2[a] += sz2[b];
        sub2[a].insert(sub2[a].end(), sub2[b].begin(), sub2[b].end());
        for (int x : sub2[b]) {
            f(cnt[x][b], -1);
            f(cnt[x][a], 1);
        }
    }

    auto rollback = [&]() {
        assert(!stkSz.empty());
        while (stk.size() > stkSz.back()) {
            auto [a, b] = stk.back();
            stk.pop_back();
            sz2[a] -= sz2[b];
            ans -= 1LL * sz2[a] * sz2[b];
            fa2[b] = b;
            sub2[a].erase(sub2[a].end() - sz2[b], sub2[a].end());
            for (int x : sub2[b]) {
                f(cnt[x][a], -1);
                f(cnt[x][b], 1);
            }
        }
        stkSz.pop_back();
    };

    int best = 2e9 + 7;

    for (int i = 0; i < ma; ++i) {
        auto relax = [&]() {
            if (ans >= k) {
                best = min(best, (i == 0 ? 0 : ea[i - 1][0]) + (stkSz.empty() ? 0 : eb[stkSz.size() - 1][0]));
            }
        };
        while (!stkSz.empty() && ans >= k) {
            relax();
            rollback();
        }
        relax();
        if (i < ma) {
            auto [w, a, b] = ea[i];
            a = find1(a), b = find1(b);
            if (a == b) {
                continue;
            }
            if (sz1[a] < sz1[b]) {
                swap(a, b);
            }
            ans += 1LL * sz1[a] * sz1[b];
            for (auto [fx, x] : cnt[b]) {
                ans -= 1LL * cnt[a][fx] * x;
                cnt[a][fx] += x;
            }
            cnt[b].clear();
            fa1[b] = a;
            sz1[a] += sz1[b];
        }
    }

    cout << (best > 2e9 ? -1 : best) << '\n';

    return 0;
}