#include <bits/stdc++.h>
using namespace std;
#define rep(i, n)  for(long long i=0;i<(long long)(n);i++)
#define REP(i,k,n) for(long long i=k;i<(long long)(n);i++)
#define pb emplace_back
#define lb(v,k) (ll)(lower_bound(all(v),(k))-v.begin())
#define ub(v,k) (ll)(upper_bound(all(v),(k))-v.begin())
#define fi first
#define se second
#define pi M_PI
#define PQ(T) priority_queue<T>
#define SPQ(T) priority_queue<T,vector<T>,greater<T>>
#define dame(a) {out(a);return 0;}
#define decimal cout<<fixed<<setprecision(15);
#define all(a) a.begin(),a.end()
#define rsort(a) {sort(all(a));reverse(all(a));}
#define dupli(a) {sort(all(a));a.erase(unique(all(a)),a.end());}
#define popcnt __builtin_popcountll
typedef long long ll;
typedef pair<ll,ll> P;
typedef tuple<ll,ll,ll> PP;
typedef tuple<ll,ll,ll,ll> PPP;
using vi=vector<ll>;
using vvi=vector<vi>;
using vvvi=vector<vvi>;
using vvvvi=vector<vvvi>;
using vp=vector<P>;
using vvp=vector<vp>;
using vb=vector<bool>;
using vvb=vector<vb>;
const ll inf=1001001001001001001;
const ll INF=1001001001;
const ll mod=1000000007;
const double eps=1e-10;
template<class T> bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;}
template<class T> bool chmax(T&a,T b){if(a<b){a=b;return true;}return false;}
template<class T> void out(T a){cout<<a<<'\n';}
template<class T> void outp(T a){cout<<'('<<a.fi<<','<<a.se<<')'<<'\n';}
template<class T> void outvp(T v){rep(i,v.size())cout<<'('<<v[i].fi<<','<<v[i].se<<')';cout<<'\n';}
template<class T> void outvvp(T v){rep(i,v.size())outvp(v[i]);}
template<class T> void outv(T v){rep(i,v.size()){if(i)cout<<' ';cout<<v[i];}cout<<'\n';}
template<class T> void outvv(T v){rep(i,v.size())outv(v[i]);}
template<class T> void yesno(T b){if(b)out("yes");else out("no");}
template<class T> void YesNo(T b){if(b)out("Yes");else out("No");}
template<class T> void YESNO(T b){if(b)out("YES");else out("NO");}
template<class T> void outset(T s){auto itr=s.begin();while(itr!=s.end()){if(itr!=s.begin())cout<<' ';cout<<*itr;itr++;}cout<<'\n';}
void outs(ll a,ll b){if(a>=inf-100)out(b);else out(a);}
ll gcd(ll a,ll b){if(b==0)return a;return gcd(b,a%b);}
ll modpow(ll a,ll b){ll res=1;a%=mod;while(b){if(b&1)res=res*a%mod;a=a*a%mod;b>>=1;}return res;}

int main(){
    ll n,K;vi m(2);cin>>n>>m[0]>>m[1]>>K;
    if(K==0)dame(0);
    vvi cost(2);
    vvp nex(2);
    vvvi con(2);
    rep(tt,2){
        vector<PP> edge(m[tt]);
        rep(i,m[tt]){
            ll a,b,c;cin>>a>>b>>c;
            edge[i]=PP(c,a-1,b-1);
        }
        sort(all(edge));
        vi par(n);rep(i,n)par[i]=i;
        vvi gr(n);rep(i,n)gr[i].pb(i);
        for(auto x:edge){
            ll t,a,b;tie(t,a,b)=x;
            if(par[a]==par[b])continue;
            cost[tt].pb(t);
            a=par[a];b=par[b];
            if(gr[a].size()>gr[b].size())swap(a,b);
            nex[tt].pb(a,b);
            con[tt].pb(gr[a]);
            for(ll x:gr[a])gr[b].pb(x);
            for(ll x:gr[a])par[x]=b;
        }
    }
    vi cntA(n,1),cntB(n,1);
    map<P,ll> cntC;
    rep(i,n)cntC[P(i,i)]=1;
    ll a=0,b=0,c=0;
    vvi par(2,vi(n));rep(i,2)rep(j,n)par[i][j]=j;
    auto merge=[&](ll tt,ll i){
        for(ll x:con[tt][i]){
            ll A=par[0][x],B=par[1][x];
            cntA[A]--;cntB[B]--;cntC[P(A,B)]--;
            a-=cntA[A];b-=cntB[B];c-=cntC[P(A,B)];

            if(tt==0)assert(A==nex[tt][i].fi);
            else assert(B==nex[tt][i].fi);
            par[tt][x]=nex[tt][i].se;

            A=par[0][x];B=par[1][x];
            a+=cntA[A];b+=cntB[B];c+=cntC[P(A,B)];
            cntA[A]++;cntB[B]++;cntC[P(A,B)]++;
        }
    };
    auto unmerge=[&](ll tt,ll i){
        for(ll x:con[tt][i]){
            ll A=par[0][x],B=par[1][x];
            cntA[A]--;cntB[B]--;cntC[P(A,B)]--;
            a-=cntA[A];b-=cntB[B];c-=cntC[P(A,B)];

            if(tt==0)assert(A==nex[tt][i].se);
            else assert(B==nex[tt][i].se);
            par[tt][x]=nex[tt][i].fi;

            A=par[0][x];B=par[1][x];
            a+=cntA[A];b+=cntB[B];c+=cntC[P(A,B)];
            cntA[A]++;cntB[B]++;cntC[P(A,B)]++;
        }
    };
    ll l=0;
    while(l<cost[1].size()&&a+b-c<K){
        merge(1,l);l++;
    }
    ll ans=inf;
    if(a+b-c>=K)ans=cost[1][l-1];
    rep(i,cost[0].size()){
        merge(0,i);
        while(a+b-c>=K&&l>0){
            unmerge(1,l-1);
            l--;
        }
        if(l<cost[1].size()){
            chmin(ans,cost[0][i]+cost[1][l]);
            if(a+b-c>=K)chmin(ans,cost[0][i]);
        }
    }
    out(ans);
}