#include<bits/stdc++.h>
using namespace std;
#define int long long
#define ii pair<int,int>
#define aa array<int,3>
#define fir first
#define sec second
#define pb push_back
const int maxn=2e5;
int n,a,b,k;
vector<aa>edgea,edgeb;
int dsu[maxn+2],tot;
vector<int>node[maxn+2];
int fin(int a){
return dsu[a];
}
vector<aa> merg(int a,int b){
a=dsu[a],b=dsu[b];
if(a==b)return{};
tot+=(node[a].size() * node[b].size());
vector<aa>event;
if(node[a].size()>node[b].size())swap(a,b);
for(auto x : node[a]){
node[b].pb(x);
event.pb({x,a,b});
dsu[x]=b;
}
node[a].clear();
return event;
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
cin>>n>>a>>b>>k;
for(int q=1;q<=a;q++){
int u,v,w;
cin>>u>>v>>w;
edgea.pb({w,u,v});
}
for(int q=1;q<=b;q++){
int u,v,w;
cin>>u>>v>>w;
edgeb.pb({w,u,v});
}
sort(edgea.begin(),edgea.end());
sort(edgeb.begin(),edgeb.end());
tot=0;int ans=1e18;
for(int q=1;q<=n;q++){
dsu[q]=q; node[q]={q};
}
vector<aa>eva[a+1]; int hasa[a+1];
for(int q=0;q<edgea.size();q++){
auto [w,u,v]=edgea[q];
eva[q+1]=merg(u,v);
hasa[q+1]=tot;
if(tot>=k)ans=min(ans,w);
}
tot=0;
for(int q=1;q<=n;q++){
dsu[q]=q; node[q]={q};
}
vector<aa>evb[b+1]; int hasb[b+1];
for(int q=0;q<edgeb.size();q++){
auto [w,u,v]=edgeb[q];
evb[q+1]=merg(u,v);
hasb[q+1]=tot;
if(tot>=k)ans=min(ans,w);
}
int para[n+1],parb[n+1];
map<ii,int>mp;
int sama=0,pos=b;
for(int q=1;q<=n;q++){
para[q]=q; parb[q]=dsu[q];
mp[{para[q],parb[q]}]++;
}
for(int q=1;q<=a;q++){
for(auto [u,prv,nxt] : eva[q]){
mp[{para[u],parb[u]}]--;
sama-=mp[{para[u],parb[u]}];
para[u]=nxt;
sama+=mp[{para[u],parb[u]}];
mp[{para[u],parb[u]}]++;
}
// cout<<q<<" "<<sama<<" k "<<hasb[pos]<<endl;
while(pos && hasa[q]+hasb[pos]-sama>=k){
// cout<<q<<" "<<pos<<" "<<hasa[q]+hasb[pos]-sama<<endl;
for(auto [u,prv,nxt] : evb[pos]){
mp[{para[u],parb[u]}]--;
sama-=mp[{para[u],parb[u]}];
parb[u]=prv;
sama+=mp[{para[u],parb[u]}];
mp[{para[u],parb[u]}]++;
}
pos--;
}
if(pos<n){
ans=min(ans,edgea[q-1][0]+edgeb[pos][0]);
}
}
cout<<ans<<endl;
}
