#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
const int N=1000+13;
int e[N][N],a[N],b[N],cnt[N],sum[N],n,root,tot,clo,ans;
double w[N];
inline bool cmp(int x,int y){return w[x]>w[y];}
void dfs1(int u){
	cnt[u]=1,sum[u]=a[u];
	for(int i=1;i<=b[u];++i){
		int v=e[u][i];
		dfs1(v);
		cnt[u]+=cnt[v],sum[u]+=sum[v];
	}
	w[u]=(double)sum[u]/cnt[u];
}
void dfs2(int u){
	++clo,ans+=clo*a[u];
	sort(e[u]+1,e[u]+b[u]+1,cmp);
	for(int i=1;i<=b[u];++i) dfs2(e[u][i]);
}
inline void clear(){
	ans=clo=tot=0;
	memset(b,0,sizeof(b));
	memset(e,0,sizeof(e));
}
int main(){
	while(scanf("%d%d",&n,&root)==2&&(n||root)){
		clear();
		for(int i=1;i<=n;++i) scanf("%d",&a[i]);
		for(int i=1,u,v;i<n;++i){
			scanf("%d%d",&u,&v);
			e[u][++b[u]]=v;
		}
		dfs1(root);
		dfs2(root);
		printf("%d\n",ans);
	} 
	return 0;
}

UVA1205,WA,求助各位巨佬，感激不尽。