#include <bits/stdc++.h>
using namespace std;

#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define pb push_back
#define x first
#define y second
#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--)

typedef long long ll;
typedef double db;
typedef long double LD;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<db, db> pdd;

#ifdef ONPC
mt19937 rnd(228);
#endif

int n;
vector<bool> C;
vector<vector<int>> G;

int dfs(int v, int pr, int d)
{
	if(d == 0)
		return 0;
	int res = 0;
	if(C[v])
		++res;
	for(auto to: G[v])
	{
		if(to != pr)
			res += dfs(to, v, d-1);
	}
	return res;
}

int g(const vector<int>& verts)
{
	int D = sz(verts)-1;
	int d1 = 1;
	int d2 = D-1;
	int res = 2;
	FOR(i, 1, sz(verts)-1)
	{
		int v = verts[i];
		if(C[v])
			++res;
		for(auto to: G[v])
		{
			if(to != verts[i-1] && to != verts[i+1])
			{
				res += dfs(to, v, min(d1, d2));
			}
		}
		d1 += 1;
		d2 -= 1;
	}
	return res;
}

bool get_path(int v, int pr, int last, vector<int>& verts)
{
	verts.pb(v);
	if(v == last)
		return true;
	for(auto to: G[v])
	{
		if(to != pr)
		{
			if(get_path(to, v, last, verts))
				return true;
		}
	}
	verts.pop_back();
	return false;
}

int f(int m)
{
	int res = INT32_MAX;
	FOR(i,0,n)
	{
		FOR(j,i+1,n)
		{
			if(C[i] && C[j])
			{
				vector<int> verts;
 				get_path(i, -1, j, verts);
 				int max_m = g(verts);
 				if(max_m >= m)
					res = min(res, sz(verts)-1);
			}
		}
	}
	return res;
}

int solve()
{
	int m;
	if(!(cin >> n >> m))
		return 1;
	C = vector<bool>(n, false);
	FOR(i,0,n)
	{
		int val;
		cin >> val;
		C[i] = val;
	}
	G = vector<vector<int>>(n);
	FOR(_,0,n-1)
	{
		int u, v;
		cin >> u >> v;
		--u, --v;
		G[u].pb(v);
		G[v].pb(u);
	}
	if(m == 1)
		cout << "0\n";
	else
		cout << f(m) << '\n';
		
	return 0;
}

int32_t main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	int TET = 1e9;
	// cin >> TET;
	for (int i = 1; i <= TET; i++)
	{
		if (solve())
			break;
			
		#ifdef ONPC
			cerr << "_________________________\n";
		#endif
	}
	#ifdef ONPC
			cerr << "\nfinished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec\n";
	#endif
}