#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
using namespace std;

typedef long long int lli;

const lli inf = 27070509170705;

vector<lli> W;
vector<vector<lli>> graph;

pair<lli, lli> dfs(lli node, lli par, lli alow)
{
	if(W[node] > alow) return {0, inf};
	else
	{
		vector<pair<lli, lli>> S;
		for(auto it: graph[node])
		{
			if(it != par) S.push_back(dfs(it, node, alow));
		}
		sort(S.begin(), S.end());

		lli cur_size = W[node], del = 0;
		for(auto it: S)
		{
			if(cur_size+it.first <= alow)
			{
				cur_size += it.first;
			}
			else del++;
			del += it.second;
		}
		//cout << node << " " << cur_size << " " << del << "\n";
		return {cur_size, del};
	}
}

lli f(lli v)
{
	pair<lli, lli> res = dfs(0, -1, v);
	//cout << v << " " << res.first << " " << res.second << "\n";
	return res.second;
}

int main(void)
{
	lli n, k, u, v;
	scanf("%lld%lld", &n, &k);
	W.clear(); W.resize(n);
	graph.clear(); graph.resize(n);
	for(lli i = 0;i < n;i++) scanf("%lld", &W[i]);

	for(lli i = 1;i < n;i++)
	{
		scanf("%lld%lld", &u, &v);
		u--; v--;
		graph[u].push_back(v);
		graph[v].push_back(u);
	}

	lli L = 1, R = inf-1, mid;
	while(L <= R)
	{
		mid = (L+R)/2;
		//cout << mid << " " << f(mid) << "\n";
		if(f(mid) >= k)
		{
			L = mid+1;
		}
		else R = mid-1;
	}
	printf("%lld\n", R+1);
}