#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
#define i128 __int128
#define pii pair<int, int>
#define pll pair<ll, ll>
#define all(x) (x).begin(), (x).end()
bool be;
#define int ll
constexpr int N = 6e5 + 5, inf = 1e9 + 9;
int n, a, b, cnt, fa[N], siz[N], in[N], tot;
ll k, sum;
unordered_map<int, int>mp[N];
vector<int>v[N], e[N];
struct edge {
	int u, v, w;
}e1[N], e2[N], tmp[N];
int find(int k)
{
	return fa[k] == k ? k : fa[k] = find(fa[k]);
}
ll h(int n)
{
	return (ll) n * (n - 1) / 2;
}
ll work(edge *e, int &m)
{
	cnt = 0;
	for (int i = 1; i <= n; ++i) fa[i] = i, siz[i] = 1;
	sort(e + 1, e + 1 + m, [](edge a, edge b) {
		return a.w < b.w;
	});
	for (int i = 1; i <= m; ++i) {
		int fx = find(e[i].u), fy = find(e[i].v);
		if (fx != fy) {
			fa[fx] = fy;
			siz[fy] += siz[fx];
			tmp[++cnt] = e[i];
		}
	}
	m = cnt;
	copy(tmp + 1, tmp + 1 + m, e + 1);
	e[m + 1] = {0, 0, 0};
	ll ans = 0;
	for (int i = 1; i <= n; ++i) {
		if (find(i) == i) {
			ans += h(siz[i]);
		}
	}
	return ans;
}
int dfs(int u, int f, int c)
{
	if (in[u]) {
		sum += h(mp[find(u)][in[u]]) + h(mp[find(u)][c]);
		--mp[find(u)][in[u]];
		++mp[find(u)][c];
		sum -= h(mp[find(u)][in[u]]) + h(mp[find(u)][c]);
	} else {
		++mp[find(u)][c];
	}
	in[u] = c;
	int ans = 1;
	for (int v : e[u]) {
		if (v != f) {
			ans += dfs(v, u, c);
		}
	}
	return ans;
}
bool en;
signed main()
{
#ifdef IAKIOI
	cerr << (&be - &en) / 1024.0 / 1024 << " MB\n----------------------------" << endl;
	freopen("in.in", "r", stdin);
	// freopen("out.out", "w", stdout);
#endif
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cin >> n >> a >> b >> k;
	for (int i = 1; i <= a; ++i) {
		cin >> e1[i].u >> e1[i].v >> e1[i].w;
	}
	for (int i = 1; i <= b; ++i) {
		cin >> e2[i].u >> e2[i].v >> e2[i].w;
	}
	work(e1, a);
	sum = work(e2, b);
	sort(e2 + 1, e2 + 1 + b, [](edge a, edge b) {
		return a.w > b.w;
	});
	for (int i = 1; i <= b; ++i) {
		e[e2[i].u].emplace_back(e2[i].v);
		e[e2[i].v].emplace_back(e2[i].u);
	}
	for (int i = 1; i <= n; ++i) {
		fa[i] = i, siz[i] = 1;
		v[i].emplace_back(i);
	}
	for (int i = 1; i <= n; ++i) {
		if (!in[i]) {
			dfs(i, 0, ++tot);
		}
	}
	int ans = inf;
	for (int i = 0, j = 1; ; ++i) {
		while (sum >= k) {
			// cerr << i << ' ' << j << ' ' << e1[i].w << ' ' << e2[j].w << ' ' << sum << '\n';
			ans = min(ans, e1[i].w + e2[j].w);
			if (j > b) break;
			int szx = dfs(e2[j].u, e2[j].v, ++tot);
			int szy = dfs(e2[j].v, e2[j].u, ++tot);
			sum -= h(szx + szy);
			sum += h(szx) + h(szy);
			++j;
			// cerr << i << ' ' << j << ' ' << e1[i].w << ' ' << e2[j].w << ' ' << sum << '\n';
 		}
 		if (i == a) break;
		int fx = find(e1[i + 1].u), fy = find(e1[i + 1].v);
		if (siz[fx] > siz[fy]) swap(fx, fy);
		fa[fx] = fy;
		sum -= h(siz[fx]) + h(siz[fy]);
		siz[fy] += siz[fx];
		sum += h(siz[fy]);
		for (int x : v[fx]) {
			v[fy].emplace_back(x);
			sum += h(mp[fx][in[x]]) + h(mp[fy][in[x]]);
			--mp[fx][in[x]];
			++mp[fy][in[x]];
			sum -= h(mp[fx][in[x]]) + h(mp[fy][in[x]]);
		}
		unordered_map<int, int>_;
		mp[fx].swap(_);
	}
	cout << (ans == inf ? -1 : ans) << endl;
	return 0;
}