#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <unordered_map>
#define int long long
using namespace std;

int n,A,B,K,m;
int fa[200005];
int ww[200005];
int ss[200005];
int bl[200005];
vector <int> g[200005];
vector <int> d[200005];
vector <int> p[200005];
struct node{int u,v,w;};
node a[200005];
node b[200005];
unordered_map <int,int> mp[200005];

inline int Find(int x){return fa[x]==x?x:fa[x]=Find(fa[x]);}

inline void in(int &n){
	n=0;
	char c=getchar();
	while(c<'0' || c>'9') c=getchar();
	while(c>='0'&&c<='9') n=n*10+c-'0',c=getchar();
	return ;
}

signed main(){
	in(n),in(A),in(B),in(K);
	for(int i=1;i<=A;i++) in(a[i].u),in(a[i].v),in(a[i].w);
	for(int i=1;i<=B;i++) in(b[i].u),in(b[i].v),in(b[i].w);
	sort(a+1,a+1+A,[](node p,node q){return p.w<q.w;});
	sort(b+1,b+1+B,[](node p,node q){return p.w<q.w;});
	for(int i=1;i<=n;i++) fa[i]=i,g[i].emplace_back(i);
	for(int i=1;i<=B;i++){
		int r=i;
		while(r<=B&&b[i].w==b[r].w) r++;
		r--;
		ww[++m]=b[i].w;
		ss[m]=ss[m-1];
		while(i<=r){
			int u=Find(b[i].u),v=Find(b[i].v);
			i++;
			if(u==v) continue;
			ss[m]+=1ll*g[v].size()*g[u].size();
			if(g[v].size()>g[u].size()) swap(u,v);
			for(int vv:g[v]) g[u].emplace_back(vv);
			fa[v]=u;
			p[m].emplace_back(v);
		}
		i--;
	}
	for(int i=1;i<=n;i++) bl[i]=Find(i);
	for(int i=1;i<=n;i++) fa[i]=i,d[i].emplace_back(i),mp[i][bl[i]]=1;
	a[A+1].w=1e15;
	int ans=1e18,X=0,Y=0,pos=1;
	for(int i=m;i>=1;i--){
		while(pos<=A&&X+ss[i]-Y<K){
			int u=Find(a[pos].u),v=Find(a[pos].v);
			pos++;
			if(u==v) continue;
			if(d[v].size()>d[u].size()) swap(u,v);
			X+=1ll*d[v].size()*d[u].size();
			for(int vv:d[v]){
				mp[v][bl[vv]]--;
				Y-=mp[v][bl[vv]];
				Y+=mp[u][bl[vv]];
				mp[u][bl[vv]]++;
				d[u].emplace_back(vv);
			}
			fa[v]=u;
		}
		if(X+ss[i]-Y>=K) ans=min(ans,ww[i]+a[pos-1].w);
		else break;
		for(int v:p[i]){
			for(int vv:g[v]){
				mp[Find(vv)][bl[vv]]--;
				Y-=mp[Find(vv)][bl[vv]];
				bl[vv]=v;
				Y+=mp[Find(vv)][bl[vv]];
				mp[Find(vv)][bl[vv]]++;
			}
		}
	}
	printf("%lld\n",ans>2e9?-1:ans);

	return 0;
}