#include<bits/stdc++.h>
using namespace std;
typedef long double ld;

inline int rd() {
	int x = 0;
	bool f = 0;
	char c = getchar();
	for (; !isdigit(c); c = getchar()) f |= (c == '-');
	for (; isdigit(c); c = getchar()) x = x * 10 + (c ^ 48);
	return f ? -x : x;
}

#define N 100007

#define fr first
#define sc second
#define mp make_pair
#define pii pair<int, int>

ld a[N], ans = 0.0;

vector<int> e[N];

inline ld sqr(ld x) {return x * x;}

void dfs(int u, int fa) {
	ld mx = 0, mn = 0;
	for (auto v : e[u])
		if (v != fa) {
			dfs(v, u);
			ans = max(ans, sqr((a[u] + a[v]) / 2));
			if (u != 1) ans = max(ans, sqr((a[u] + a[fa] + a[v]) / 3));
			ans = max(ans, sqr((a[u] + a[v] + mx) / 3));
			ans = max(ans, sqr((a[u] + a[v] + mn) / 3));
			mx = max(mx, a[v]);
			mn = min(mn, a[v]);
		}
}

int main() {
	int n = rd();
	for (int i = 1; i <= n; ++i) a[i] = rd();
	for (int i = 1; i < n; ++i) {
		int u = rd(), v = rd();
		e[u].push_back(v); e[v].push_back(u);
	}
	dfs(1, 1);
	printf("%.6Lf\n", ans / 4.0);
	return 0;
}