#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=4e5+5,inf=2e9+7;
int n,A,B,Sz[N],sz[N],fa[N],Fa[N][19],tot,ans=inf;
int dfn[N],in[N],out[N],nw,Rt,ln[N];
int rt[N],ls[N*40],rs[N*40],ct[N*40],cnt;
vector<int>e[N],w[N];
ll K,sum,va[N];
struct edge{
	int x,y,z;
	bool operator <(const edge a)const{return z<a.z;}
}ea[N],eb[N];
int gf(int x){
	return fa[x]==x?fa[x]:fa[x]=gf(fa[x]);
}
void dfs1(int x){
	for(int i=1;i<19;++i)Fa[x][i]=Fa[Fa[x][i-1]][i-1];
	if(x<=n){
		in[x]=out[x]=dfn[x]=++dfn[0];
		return;
	}
	in[x]=dfn[0];
	for(auto v:e[x])dfs1(v);
	out[x]=dfn[0];
}
void ins(int &k,int l,int r,int x){
	k=++cnt,ct[k]=1;
	if(l==r)return;
	int mid=l+r>>1;
	if(x<=mid)ins(ls[k],l,mid,x);
	else ins(rs[k],mid+1,r,x);
}
int merge(int x,int y){
	if(!x||!y)return x|y;
	ls[x]=merge(ls[x],ls[y]);
	rs[x]=merge(rs[x],rs[y]);
	ct[x]=ct[x]+ct[y];
	return x;
}
int query(int k,int l,int r,int x,int y){
	if(!k)return 0;
	if(x<=l&&r<=y)return ct[k];
	int mid=l+r>>1,res=0;
	if(x<=mid)res+=query(ls[k],l,mid,x,y);
	if(y>mid)res+=query(rs[k],mid+1,r,x,y);
	return res;
}
void chg(int x){
	int c=gf(x),u=dfn[x];
	for(int i=18;~i;--i)if(Fa[x][i]&&Fa[x][i]<=nw)x=Fa[x][i];
	if(x<=n)return;
	sum-=query(rt[c],1,n,in[x],out[x]);
	if(out[e[x][0]]>=u)va[x]-=query(rt[c],1,n,in[e[x][1]],out[e[x][1]]);
	else va[x]-=query(rt[c],1,n,in[e[x][0]],out[e[x][0]]);
}
void dfs2(int x,int y){
	if(x<=n){
		va[Rt]-=query(rt[gf(x)],1,n,in[e[Rt][y]],out[e[Rt][y]]);
		return;
	}
	for(auto v:e[x])dfs2(v,y);
}
void calc(int x){
	if(x<=n)return;
	Rt=x;
	if(Sz[e[x][0]]<Sz[e[x][1]])dfs2(e[x][0],1);
	else dfs2(e[x][1],0);
	sum+=va[x];
}
int main(){
	scanf("%d%d%d%lld",&n,&A,&B,&K);
	tot=n;
	for(int i=1;i<=A;++i)scanf("%d%d%d",&ea[i].x,&ea[i].y,&ea[i].z);
	for(int i=1;i<=B;++i)scanf("%d%d%d",&eb[i].x,&eb[i].y,&eb[i].z);
	for(int i=1;i<=n;++i)Sz[i]=1,fa[i]=i;
	sort(ea+1,ea+A+1);
	sort(eb+1,eb+B+1);
	for(int i=1;i<=A;++i){
		int x=gf(ea[i].x),y=gf(ea[i].y);
		if(x==y)continue;
		++tot,e[tot].push_back(x),e[tot].push_back(y);
		Sz[tot]=Sz[x]+Sz[y];
		ln[tot]=ea[i].z;
		sum+=(va[tot]=1ll*Sz[x]*Sz[y]);
		fa[x]=fa[y]=Fa[x][0]=Fa[y][0]=fa[tot]=tot;
	}
	for(int i=tot;i;--i)if(!Fa[i][0])dfs1(i);
	for(int i=1;i<=n;++i)ins(rt[i],1,n,dfn[i]);
	nw=tot;
	if(sum>=K)ans=ln[nw];
	for(int i=1;i<=n;++i)fa[i]=i,sz[i]=1,w[i].emplace_back(i);
	for(int i=1;i<=B;++i){
		int x=gf(eb[i].x),y=gf(eb[i].y);
		if(x==y)continue;
		if(sz[x]>sz[y])swap(x,y);
		sum+=1ll*sz[x]*sz[y];
		fa[x]=y,sz[y]+=sz[x];
		for(auto v:w[x])chg(v),w[y].emplace_back(v);
		rt[y]=merge(rt[y],rt[x]);
		while(nw>n&&sum-va[nw]>=K){
			sum-=va[nw];
			calc(e[nw][0]);
			calc(e[nw][1]);
			--nw;
		}
		if(sum>=K)ans=min(ans,eb[i].z+ln[nw]);
	}
	if(ans==inf)puts("-1");
	else printf("%d\n",ans);
	return 0;
}