//code by Emissary
#include<bits/stdc++.h>

#define fi first
#define se second
#define vc vector
#define db double
#define ll long long
#define mk make_pair
#define pb push_back
#define PI pair<int,int>
#define ull unsigned long long
#define err cerr << "   -_-   " << endl
#define debug cerr << " ------------------- " << endl

#define input(x) freopen(#x".in","r",stdin)
#define output(x) freopen(#x".out","w",stdout)

#define NO puts("No")
#define YES puts("Yes")

//#define int long long

using namespace std;

namespace IO{
	inline ll read(){
		ll X=0, W=0; char ch=getchar();
		while(!isdigit(ch)) W|=ch=='-', ch=getchar();
		while(isdigit(ch)) X=(X<<1)+(X<<3)+(ch^48), ch=getchar();
		return W?-X:X;
	}
	inline void write(int x){
		if(x<0) x=-x, putchar('-');
		if(x>9) write(x/10);
		putchar(x%10+'0');
	}
	inline void sprint(int x){write(x), putchar(32);}
	inline void eprint(int x){write(x), putchar(10);}
}using namespace IO;

const int inf = 2e9;
const int MAXN = 4e5+5;
const int mod = 998244353;
//const int mod = 1e9+7;

int tot, ans=2e9+2;
int n, A, B, lc[MAXN], rc[MAXN], id[MAXN];
int fa[MAXN], siz[MAXN], val[MAXN], bel[MAXN], minid[MAXN];

ll now, K;

unordered_map<int,int> s[MAXN];

vc<int> node[MAXN];

struct edge{
	int u, v, w;
	inline bool friend operator < (const edge &x, const edge &y){return x.w<y.w;}
}p[MAXN], q[MAXN];

inline ll C(int x){return 1ll*x*(x-1)/2;}

inline int find(int x){return x==fa[x]?x:fa[x]=find(fa[x]);}

inline void add(int i){
	int x=q[i].u, y=q[i].v;
	x=find(x), y=find(y);
	if(x==y) return ;
	now-=C(node[x].size()); now-=C(node[y].size());
	if(node[x].size()>node[y].size()) swap(x,y);
	for(auto i:node[x]) node[y].pb(i), bel[i]=y; now+=C(node[y].size());
	for(auto i:s[x]) if(i.se) now+=C(i.se), now+=C(s[y][i.fi]), s[y][i.fi]+=i.se, now-=C(s[y][i.fi]); fa[x]=y;
	s[x].clear(); node[x].clear(); node[x].shrink_to_fit();
	return ;
}

inline void dfs(int x, int v, int k){
	if(x<=n){
		int t=bel[x];
		now+=C(s[t][k]);
		s[t][k]--; now-=C(s[t][k]);
		now+=C(s[t][v]);
		s[t][v]++; now-=C(s[t][v]);
		return ;
	}
	else dfs(lc[x],v,k), dfs(rc[x],v,k);
}

signed main(){
	n=read(), A=read(), B=read(), K=read(); tot=n;
	for(int i=1;i<=n;++i) fa[i]=i, siz[i]=1, node[i].pb(i), bel[i]=i;
	for(int i=1;i<=A;++i) p[i].u=read(), p[i].v=read(), p[i].w=read();
	for(int i=1;i<=B;++i) q[i].u=read(), q[i].v=read(), q[i].w=read();
	sort(p+1,p+1+A); sort(q+1,q+1+B);
	for(int i=1;i<=A;++i){
		int x=p[i].u, y=p[i].v;
		x=find(x), y=find(y);
		if(x==y) continue;
		++tot; val[tot]=p[i].w;
		if(siz[x]<siz[y]) swap(x,y);
		lc[tot]=x, rc[tot]=y, minid[tot]=id[y]; 
		id[tot]=id[x], siz[tot]=siz[x]+siz[y], fa[x]=fa[y]=fa[tot]=tot;
		now-=C(siz[x]); now-=C(siz[y]); now+=C(siz[tot]);
	}
	int r=1;
	for(int i=1;i<=n;++i) s[i][find(i)]=1;
	for(int i=1;i<=n;++i) fa[i]=i;
	for(int i=tot;i>=n;--i){
		while(r<=B && now<K) add(r), r++;
		if(now<K) break; ans=min(ans,val[i]+q[r-1].w);
		//cout << i << ' ' << q[r-1].w << ' ' << now << endl;
		if(i==n) break; 
		now-=C(siz[i]); 
		now+=C(siz[lc[i]]); now+=C(siz[rc[i]]);
		//cerr << "now=" << now << endl;
		dfs(rc[i],minid[i],id[i]);
	}
	eprint(ans>inf?-1:ans);
	return 0;
}