#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<deque>
#include<iostream>
#include<list>
#include<map>
#include<queue>
#include<set>
#include<vector>

#define MAX(x,y) ((x>y)?x:y)
#define min(x,y) ((x<y)?x:y)
typedef long long ll;

using namespace std;

struct edge{
	int a,b,l,c;
	bool operator < (edge p) const {return (c<p.c);}
};
struct edge2{
	int to,cost;
	edge2(int a,int b){to=a;cost=b;}
	bool operator < (edge2 q) const {return (to<q.to);}
};
struct edge3{int to,cost;};
struct P{
	int min,v;
	P(int a,int b){min=a,v=b;}
	bool operator < (P p) const {return (min>p.min);}
};

//Dijkstra
edge e[200005],e2[100005];
int fest[100005],cost[100005];
int vis[100005],dis[100005];
int n,en;
vector<edge2> G[100005];
priority_queue<P> que;
void dijkstra(int x){
	int i,v;
	
	while(!que.empty()){
		P p=que.top();
		que.pop();
		v=p.v;
		if(dis[v]<p.min)continue;
		for(i=0;i<G[v].size();i++){
			edge2 e=G[v][i];
			if(dis[e.to]>dis[v]+e.cost){
				dis[e.to]=dis[v]+e.cost;
				que.push(P(dis[e.to],e.to));
			}
		}
	}
	for(i=1;i<=n;i++){
		//printf("%2d %d\n",i,dis[i]);
		//cost[i]=min(cost[i],dis[i]);
		cost[i]=dis[i];
	}
}

//Union-Find
int f[100005];
void init(int n){
	for(int i=1;i<=n;i++)f[i]=i;
	return;
}
int find(int x){
	if(f[x]!=x)f[x]=find(f[x]);
	return f[x];
}
void unite(int x,int y){
	int p=find(x),q=find(y);
	f[p]=q;
	return;
}

//LCA
int depth[100005];
edge3 parents[20][100005];
int dfs(int v,int p,int d){
	parents[0][v].to=p;
	//parents[0][v].cost=min(cost[v],(p==-1)?(1000000000):cost[p]);
	if(p==-1)parents[0][v].cost=cost[v];
	else parents[0][v].cost=min(cost[v],cost[p]);
	depth[v]=d;
	for(int i=0;i<G[v].size();i++){
		edge2 ee=G[v][i];
		if(ee.to!=p)dfs(ee.to,v,d+1);
	}
}
void init2(int root){
	dfs(root,-1,0);
	for(int k=0;k<18;k++){
		for(int v=1;v<=n;v++){
			if(parents[k][v].to<0)parents[k+1][v].to=-1;
			else{
				parents[k+1][v].to=parents[k][parents[k][v].to].to;
				parents[k+1][v].cost=min(parents[k][v].cost,parents[k][parents[k][v].to].cost);
			}
		}
	}
}
int lca(int a,int b){
	int c,k,res;
	res=min(cost[a],cost[b]);
	if(depth[a]>depth[b])c=a,a=b,b=c;
	for(k=0;k<18;k++){
		if(((depth[b]-depth[a])>>k&1)){
			res=min(res,parents[k][b].cost);
			b=parents[k][b].to;
		}
	}
	if(a==b)return min(res,cost[a]);
	for(k=17;k>=0;k--){
		if(parents[k][a].to!=parents[k][b].to){
			res=min(res,min(parents[k][a].cost,parents[k][b].cost));
			a=parents[k][a].to;
			b=parents[k][b].to;
		}
	}
	return min(res,parents[0][a].cost);
}
int main(){
	int i,j,k,m,K,q,s,t;
	priority_queue<edge> que2;
	
	scanf("%d%d%d%d",&n,&m,&K,&q);
	for(i=0;i<m;i++){
		scanf("%d%d%d",&e[i].a,&e[i].b,&e[i].l);
		G[e[i].a].push_back(edge2(e[i].b,e[i].l));
		G[e[i].b].push_back(edge2(e[i].a,e[i].l));
	}
	//Dijkstra
	fill(cost,cost+n+1,1000000000);
	fill(dis,dis+n+1,1000000000);
	for(i=0;i<K;i++){
		scanf("%d",&fest[i]);
		dis[fest[i]]=0;
		que.push(P(0,fest[i]));
	}
	dijkstra(fest[0]);
	
	for(i=1;i<=n;i++){
		//printf("%2d %d\n",i,cost[i]);
		G[i].clear();
	}
	//CreateTree
	init(n);
	en=0;
	for(i=0;i<m;i++){
		e[i].c=min(cost[e[i].a],cost[e[i].b]);
		que2.push(e[i]);
	}
	while(!que2.empty()){
		edge ee=que2.top();
		que2.pop();
		if(find(ee.a)!=find(ee.b)){
			unite(ee.a,ee.b);
			e2[en++]=ee;
			G[ee.a].push_back(edge2(ee.b,ee.c));
			G[ee.b].push_back(edge2(ee.a,ee.c));
		}
	}
	
	//LCA
	init2(1);
	/*
	printf("en:%d\n",en);
	for(i=0;i<en;i++)printf("%d %d\n",e2[i].a,e2[i].b);
	for(i=1;i<=n;i++){
		printf("%d(dep:%d):",i,depth[i]);
		for(j=0;j<3;j++)printf("%2d(%2d) ",parents[j][i].to,parents[j][i].cost);
		printf("\n");
	}
	*/
	
	while(q--){
		scanf("%d%d",&s,&t);
		//printf("%d %d ->lca %d\n",s,t,lca(s,t));
		printf("%d\n",lca(s,t));
	}
	
	return 0;
}

Measured memory_bytes: 36032