#include <bits/stdc++.h>
using namespace std;
#define int long long
int const N=4e5+5;
int const inf=2e9+7;
int n,a,b,k;
int rep[N];
vector<int> st[N];
signed main(){
cin>>n>>a>>b>>k;
for (int i = 0; i <=n; ++i)
{
rep[i]=i;
st[i].push_back(i);
}
vector<vector<int>> edg1,edg2;
for (int i = 0; i < a; ++i)//odd
{
int u,v,l;
cin>>u>>v>>l;
edg1.push_back({l,u,v});
}
for (int i = 0; i < b; ++i)//even
{
int u,v,l;
cin>>u>>v>>l;
edg2.push_back({l,u,v});
}
vector<pair<int,int>> lst1,lst2;
sort(edg1.begin(), edg1.end());
sort(edg2.begin(), edg2.end());
lst1.push_back({0,0});
lst2.push_back({0,0});
int tot1=0,tot2=0;
for (int i = 0; i < a; ++i)
{
int u=edg1[i][1],v=edg1[i][2],l=edg1[i][0];
u=rep[u];
v=rep[v];
if(u==v)
continue;
if(st[u].size()<st[v].size())
swap(u,v);
int c=(st[u].size());
c*=(st[v].size());
tot1+=c;
for(int i:st[v]){
rep[i]=u;
st[u].push_back(i);
}
st[v].clear();
lst1.push_back({tot1,l});
}
for (int i = 0; i < a; ++i)
{
int u=edg2[i][1],v=edg2[i][2],l=edg2[i][0];
u=rep[u];
v=rep[v];
if(u==v)
continue;
if(st[u].size()<st[v].size())
swap(u,v);
int c=(st[u].size());
c*=(st[v].size());
tot2+=c;
for(int i:st[v]){
rep[i]=u;
st[u].push_back(i);
}
st[v].clear();
lst2.push_back({tot2,l});
}
int cost=inf;
int p2=(lst2.size())-1;
for(auto [nm1,c1]:lst1){
while(p2>0 && lst2[p2-1].first+nm1>=k){
p2--;
}
if(lst2[p2].first+nm1>=k)
cost=min(cost,c1+lst2[p2].second);
}
if(cost==inf){
cout<<-1<<endl;
return 0;
}
cout<<cost<<endl;
return 0;
}
