#include <iostream>
#include <algorithm>
#include <set>
#include <map>
#include <vector>
#include <cstdio>

using namespace std;

typedef long long ll;

typedef struct Edge_tag {
	int nxt;
	int start;
	int end;
	int dis;
	Edge_tag(){}
	Edge_tag(int start_, int end_, int dis_){
		start = start_;
		end = end_;
		dis = dis_;
	}
} Edge;

inline ll comb_2(int n){
	return (ll)n * (n - 1) / 2;
}

typedef struct {
	int id;
	int root[400007];
	int val[400007];
	int ls[400007];
	int rs[400007];
	int size[400007];
	ll sum[400007];
	bool vis[400007];
	Edge edge[400007];
	vector<int> v[400007];
	
	inline void init(int n){
		for (register int i = 1; i <= n; i++){
			root[i] = i;
		}
	}
	
	int get_root(int x){
		if (root[x] == x) return x;
		return root[x] = get_root(root[x]);
	}
	
	inline void kruskal(int n, int m, int k){
		id = n;
		init(n * 2 - 1);
		for (register int i = 1; i <= n; i++){
			size[i] = 1;
			vis[i] = true;
		}
		sort(edge + 1, edge + m + 1);
		for (register int i = 1; i <= m; i++){
			int x_root = get_root(edge[i].start), y_root = get_root(edge[i].end);
			if (x_root != y_root){
				id++;
				root[x_root] = root[y_root] = id;
				val[id] = edge[i].dis;
				vis[id] = true;
				vis[x_root] = vis[y_root] = false;
				if (size[x_root] > size[y_root]){
					ls[id] = x_root;
					rs[id] = y_root;
				} else {
					ls[id] = y_root;
					rs[id] = x_root;
				}
				size[id] = size[x_root] + size[y_root];
				sum[val[id]] += comb_2(size[id]) - comb_2(size[x_root]) - comb_2(size[y_root]);
				v[val[id]].push_back(id);
			}
		}
		for (register int i = 1; i <= k; i++){
			sum[i] += sum[i - 1];
		}
	}
} Kruskal;

int dfn[400007];

typedef struct {
	bool operator ()(const int a, const int b){
		return dfn[a] > dfn[b];
	}
} Compare;

Kruskal kru1, kru2;
int w1[200007], w2[200007], pos1[400007], ref[400007], rnk[200007], pos2[400007];
bool vis1[200007], vis2[200007];
set<int> s1[200007];
set<int, Compare> s2[200007];
map<int, int> mp[200007];

bool operator <(const Edge a, const Edge b){
	return a.dis < b.dis;
}

inline int read_int(){
	int ans = 0;
	char ch = getchar();
	while (ch < '0' || ch > '9'){
		ch = getchar();
	}
	while (ch >= '0' && ch <= '9'){
		ans = ans * 10 + (ch ^ 48);
		ch = getchar();
	}
	return ans;
}

inline ll read_ll(){
	ll ans = 0;
	char ch = getchar();
	while (ch < '0' || ch > '9'){
		ch = getchar();
	}
	while (ch >= '0' && ch <= '9'){
		ans = ans * 10 + (ch ^ 48);
		ch = getchar();
	}
	return ans;
}

void dfs(int u, int n, int &id){
	if (u <= n){
		id++;
		dfn[u] = id;
		rnk[id] = u;
		return;
	}
	dfs(kru2.ls[u], n, id);
	dfn[u] = dfn[kru2.ls[u]];
	dfs(kru2.rs[u], n, id);
}

int main(){
	int n = read_int(), a = read_int(), b = read_int(), cnt1 = 0, cnt2 = 0, dfn_id = 0, set_id = 0, lst = -1, ans = 0x7fffffff;
	ll k = read_ll(), sum = 0;
	w1[++cnt1] = 0;
	for (register int i = 1; i <= a; i++){
		int u = read_int(), v = read_int(), l = read_int();
		w1[++cnt1] = l;
		kru1.edge[i] = Edge(u, v, l);
	}
	sort(w1 + 1, w1 + cnt1 + 1);
	for (register int i = 1; i <= a; i++){
		int x = lower_bound(w1 + 1, w1 + cnt1 + 1, kru1.edge[i].dis) - w1;
		while (vis1[x]) x++;
		vis1[x] = true;
		kru1.edge[i].dis = x;
	}
	kru1.kruskal(n, a, cnt1);
	w2[++cnt2] = 0;
	for (register int i = 1; i <= b; i++){
		int u = read_int(), v = read_int(), l = read_int();
		w2[++cnt2] = l;
		kru2.edge[i] = Edge(u, v, l);
	}
	sort(w2 + 1, w2 + cnt2 + 1);
	for (register int i = 1; i <= b; i++){
		int x = lower_bound(w2 + 1, w2 + cnt2 + 1, kru2.edge[i].dis) - w2;
		while (vis2[x]) x++;
		vis2[x] = true;
		kru2.edge[i].dis = x;
	}
	kru2.kruskal(n, b, cnt2);
	dfs(kru2.id, n, dfn_id);
	for (register int i = 1; i <= n; i++){
		pos1[i] = ref[i] = i;
		s1[i].insert(i);
	}
	for (register int i = 1; i <= kru2.id; i++){
		if (kru2.vis[i]){
			int t = dfn_id + 1;
			dfs(i, n, dfn_id);
			pos2[i] = ++set_id;
			for (register int j = t; j <= dfn_id; j++){
				s2[set_id].insert(rnk[j]);
				mp[rnk[j]][set_id] = 1;
			}
		}
	}
	for (register int i = 1, j = cnt2; i <= cnt1; i++){
		int size = kru1.v[i].size();
		for (register int k = 0; k < size; k++){
			int x = kru1.v[i][k];
			pos1[x] = pos1[kru1.ls[x]];
			for (register set<int>::iterator l = s1[pos1[kru1.rs[x]]].begin(); l != s1[pos1[kru1.rs[x]]].end(); l++){
				ref[*l] = pos1[x];
				s1[pos1[x]].insert(*l);
			}
			s1[pos1[kru1.rs[x]]].clear();
			for (register map<int, int>::iterator l = mp[pos1[kru1.rs[x]]].begin(); l != mp[pos1[kru1.rs[x]]].end(); l++){
				sum -= comb_2(mp[pos1[x]][l->first]);
				mp[pos1[x]][l->first] += l->second;
				sum += comb_2(mp[pos1[x]][l->first]);
			}
			mp[pos1[kru1.rs[x]]].clear();
		}
		while (j >= 1 && kru1.sum[i] + kru2.sum[j] - sum >= k){
			lst = j;
			size = kru2.v[j].size();
			for (register int k = 0; k < size; k++){
				int x = kru2.v[j][k];
				pos2[kru2.ls[x]] = pos2[x];
				pos2[kru2.rs[x]] = ++set_id;
				while (true){
					int cur = *s2[pos2[x]].begin();
					if (dfn[cur] < dfn[kru2.rs[x]]) break;
					if (--mp[ref[cur]][pos2[x]] == 0){
						mp[ref[cur]].erase(pos2[x]);
					} else {
						sum -= --mp[ref[cur]][pos2[x]];
					}
					s2[pos2[x]].erase(cur);
					sum += mp[ref[cur]][set_id]++;
					s2[set_id].insert(cur);
				}
			}
			j--;
		}
		if (lst != -1) ans = min(ans, w1[i] + w2[lst]);
	}
	if (ans == 0x7fffffff){
		cout << -1;
	} else {
		cout << ans;
	}
	return 0;
}