#include<bits/stdc++.h>
#define ll long long
#define ldb long double
#define fi first
#define se second
#define pir pair<int,int>
using namespace std;
const int maxn = 2e5 + 5;
template <class t1,class t2> inline void maxi(t1 &x,t2 y){if (x < y) x = y;}
template <class t1,class t2> inline void mini(t1 &x,t2 y){if (x > y) x = y;}
struct edge{
int u = 0,v = 0,w = 0;
bool operator <(const edge &other) const{
return (w < other.w);
}
};
vector <edge> A,B;
void input(int n,int a,int b,ll k){
while (a--){
int u,v,w;
cin >> u >> v >> w;
A.push_back({u,v,w});
}
while (b--){
int u,v,w;
cin >> u >> v >> w;
B.push_back({u,v,w});
}
}
namespace subtask1{
bool subtask1(int n,int a,int b,ll k){
return (n <= 2000);
}
const int maxN = 2e3 + 5;
const ll inf = 1e17;
int cnt[maxN][maxN],par[maxN];
vector <int> lst[maxN];
vector <edge> va,vb;
void init(int n){
for (int i = 1 ; i <= n ; i++){
par[i] = i;
lst[i].clear();
lst[i].push_back(i);
}
}
int findp(int x){
return (x == par[x]) ? x : par[x] = findp(par[x]);
}
void add(int u,int v,int w,bool state){
int x = findp(u),y = findp(v);
if (x != y){
if (lst[x].size() < lst[y].size()) swap(x,y);
for (int t1 : lst[x])
for (int t2 : lst[y]){
int x1 = min(t1,t2),x2 = max(t1,t2);
if (!state) va.push_back({x1,x2,w});
if (state) vb.push_back({x1,x2,w});
}
par[y] = x;
for (int t2 : lst[y])
lst[x].push_back(t2);
}
}
void prepare_edge(int n,int a,int b){
init(n);
sort(A.begin(),A.end());
for (edge e : A){
int u = e.u,v = e.v,w = e.w;
add(u,v,w,0);
}
init(n);
sort(B.begin(),B.end());
for (edge e : B){
int u = e.u,v = e.v,w = e.w;
add(u,v,w,1);
}
}
ll lone_case(int n,int a,int b,ll k){
//only using a
ll res = inf;
if (va.size() >= k)
mini(res,va[k - 1].w);
if (vb.size() >= k)
mini(res,vb[k - 1].w);
return res;
}
ll getsolve(int n,int a,int b,ll k){
int pointer = -1;
ll res = inf,cur = 0;
for (edge e : va){
////empty pointer
int u = e.u,v = e.v,w = e.w;
cur += (!cnt[u][v]);
cnt[u][v]++;
if (cur < k)
while (pointer < (int)vb.size() - 1 && cur < k){
pointer++;
int nu = vb[pointer].u,nv = vb[pointer].v,nw = vb[pointer].w;
cur += (!cnt[nu][nv]);
cnt[nu][nv]++;
}
while (pointer >= 0 && cur >= k){
int nu = vb[pointer].u,nv = vb[pointer].v,nw = vb[pointer].w;
//new u,v,pointer
mini(res,(ll)w + (ll)nw);
cnt[nu][nv]--;
cur -= (!cnt[nu][nv]);
pointer--;
}
}
return res;
}
ll solve(int n,int a,int b,ll k){
prepare_edge(n,a,b);
//lone state
ll res = lone_case(n,a,b,k);
mini(res,getsolve(n,a,b,k));
if (res >= inf) return -1;
return res;
}
};
int main(){
ios_base::sync_with_stdio(false);
cin.tie(0);cout.tie(0);
int n,a,b;
ll k;
cin >> n >> a >> b >> k;
input(n,a,b,k);
if (subtask1::subtask1(n,a,b,k)){
cout << subtask1::solve(n,a,b,k);
return 0;
}
return 0;
}
