#include <bits/stdc++.h>
using namespace std;
#define For(Ti,Ta,Tb) for(auto Ti=(Ta);Ti<=(Tb);++Ti)
#define Dec(Ti,Ta,Tb) for(auto Ti=(Ta);Ti>=(Tb);--Ti)
#define debug(...) fprintf(stderr,__VA_ARGS__)
#define range(Tx) begin(Tx),end(Tx)
using ll=long long;
const int N=1e6+5,Mod=1e9+7;
int n,s,a[N],fa[N],deg[N];
vector<int> e[N];
ll inv[N],f[N],g[N][2][2],ans,prob[N][2];
void dfs(int u){
	for(int v:e[u]) if(v!=fa[u]){
		fa[v]=u,dfs(v);
		if(u!=s) (f[u]+=(f[v]*inv[deg[u]-1]+inv[deg[v]]*inv[deg[u]])%Mod*inv[deg[u]])%=Mod;
	}
}
void dfs2(int u){
	ll cont=0;
	if(!(deg[u]-(u!=s))){
		For(i,0,1){
			(cont+=g[u][i][1])%=Mod;
			if(u!=s) (cont+=g[u][i][0]*inv[deg[u]]%Mod*inv[deg[fa[u]]-i+(fa[u]==s)])%=Mod;
		}
	}else if(deg[u]-(u!=s)==1){
		int son=0;
		for(int v:e[u]) if(v!=fa[u]) son=v;
		For(i,0,1) (cont+=g[u][i][1]*f[son])%=Mod;
	}
	(ans+=cont*a[u])%=Mod;
	ll sprob[2]{};
	for(int v:e[u]) if(v!=fa[u]){
		For(i,0,1){
			prob[v][i]=(f[v]*inv[deg[u]-1-i+(u==s)]+inv[deg[v]]*inv[deg[u]-i+(u==s)])%Mod*inv[deg[u]-i+(u==s)]%Mod;
			(sprob[i]+=prob[v][i])%=Mod;
		}
	}
	for(int v:e[u]) if(v!=fa[u]){
		For(i,0,1){
			if(u!=s){
				(g[v][1][1]+=g[u][i][0]*inv[deg[u]]%Mod*inv[deg[fa[u]]-i+(fa[u]==s)]%Mod*inv[deg[u]-1])%=Mod;
			}
			For(j,0,1){
				(g[v][j][0]+=g[u][i][j]*inv[deg[u]-j+(u==s)])%=Mod;
				(g[v][j][1]+=g[u][i][j]*(sprob[j]-prob[v][j]+Mod))%=Mod;
			}
		}
		dfs2(v);
	}
}
int main(){
	cin.tie(nullptr)->sync_with_stdio(false);
	cin>>n;
	For(i,1,n) cin>>a[i];
	For(i,1,n-1){
		int u,v;
		cin>>u>>v;
		e[u].push_back(v),e[v].push_back(u);
	}
	For(i,1,n) deg[i]=e[i].size();
	cin>>s;
	inv[1]=1;
	For(i,2,n) inv[i]=(Mod-Mod/i)*inv[Mod%i]%Mod;
	dfs(s);
	g[s][1][1]=1;
	dfs2(s);
	cout<<ans<<'\n';
	return 0;
}