#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef vector<LL> VL;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;
typedef double db;

const int N = 147;
const int INF = 1e9 + 47;

VI g[N];
int c[N];
int dp[N][N];
int n;

void updMax(int& a, int b)
{
	a = max(a, b);
}

void dfs(int v, int p, int dis)
{
	//cerr << v << ' ' << p << '\n';
	for (auto to : g[v])
		if (to != p)
			dfs(to, v, dis);
	dp[v][0] = c[v];
	FOR (mx, 0, dis - 1)
	{
		int sum = 0;
		int ds = min(mx, dis - mx - 2);
		for (auto to : g[v])
			if (to != p)
				sum += dp[to][ds];
		for (auto to : g[v])
			if (to != p)
				updMax(dp[v][mx + 1], dp[to][mx] - dp[to][ds] + sum + c[v]);
	}
	for (auto to : g[v])
		if (to != p)
			updMax(dp[v][dis], dp[to][dis - 1] + c[v]);
	FOR (ds, 0, dis)
		updMax(dp[v][ds + 1], dp[v][ds]);
}

int f(int dis)
{
	FOR (i, 0, N) FOR (j, 0, N) dp[i][j] = 0;
	dfs(0, 0, dis);
	//FOR (i, 0, n)
	//{
	//	FOR (ds, 0, dis + 1)
	//		cerr << dp[i][ds] << ' ';
	//	cerr << '\n';
	//}
	int ans = 0;
	FOR (i, 0, n)
		updMax(ans, dp[i][dis]);
	return ans;
}

int main()
{
	ios::sync_with_stdio(0); 
	cin.tie(0);
	
	int k;
	cin >> n >> k;
	FOR (i, 0, n) cin >> c[i];
	
	FOR (i, 0, n - 1)
	{
		int a, b;
		cin >> a >> b;
		a--, b--;
		g[a].PB(b);
		g[b].PB(a);
	}
	
	//cerr << f(4) << '\n';
	//
	//return 0;
	
	int l = -1, r = n;
	while (l + 1 < r)
	{
		int mid = (l + r) / 2;
		if (f(mid) >= k)
			r = mid;
		else
			l = mid;
	}
	cout << r << '\n';
	
	return 0;
}