/*-----------------------------
Author : TgX.2
10Ti - K28 - CHV
-----------------------------*/
#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i=(a), _b=(b);i<=_b;++i)
#define FORD(i,a,b) for(int i=(a), _b=(b);i>=_b;--i)
#define FORC(i,a,b,c) for(int i=(a), _b=(b), _c=(c);i<=_b;i+=_c)
#define FORSq(i,a,b) for(int i=(a), _b=(b);i*i<=_b;++i)
#define FORSt(i,s) for(int i=0, _s=(int)(s.size());i<_s;++i)
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define pp pop_back()
#define eb emplace_back
#define ers erase
#define ins insert
#define emp empty()
#define rvs reverse
#define BIT(x,i) (((x)>>(i))&1)
#define MASK(i) (1LL<<(i))
#define CNTBIT(x) __builtin_popcountll(x)
#define ODDBIT(x) __builtin_parityll(x)
#define FIRSTBIT(x) __builtin_ctzll(x)
#define len(x) (int)((x).size())
#define all(x) (x).begin(), (x).end()
#define alln(x,n) (x)+1, (x)+1+(n)
#define _ <<" "<<
#define __ << "\n"
#define ___ << " "
#define ____ << "\t"
#define file "temp"
#define ______________TgX______________ main()
#define int long long
#define intmax 1e9
#define intmin -1e9
#define llongmax 1e18
#define llongmin -1e18
#define memo(a, val) memset((a), (val), sizeof((a)))
using namespace std;
using namespace std::chrono;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<pii> vpii;
typedef vector<pll> vpll;
// int dx[] = {1,-1,0,0} , dy[] = {0,0,1,-1}; // 4 Direction
// int dx[] = {1,-1,0,0,1,1,-1,-1} , dy[] = {0,0,1,-1,1,-1,1,-1}; // 8 Direction
// int dx[] = {1,-1,1,-1,2,2,-2,-2} , dy[] = {2,2,-2,-2,1,-1,1,-1}; // Knight Direction
// int dx[] = {2,-2,1,1,-1,-1} , dy[] = {0,0,1,-1,1,-1}; // Hexagonal Direction
void fastio() {
if (fopen(file".inp", "r")) {
freopen(file".inp", "r", stdin);
freopen(file".out", "w", stdout);
freopen(file".debug", "w", stderr);
}
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
}
template<typename T1, typename T2> bool mini(T1 &a, T2 b)
{if(a>b) a=b; else return 0; return 1;}
template<typename T1, typename T2> bool maxi(T1 &a, T2 b)
{if(a<b) a=b; else return 0; return 1;}
/*-----------------------------*/
const int maxn = 1e5 + 7;
int n, x, a[maxn];
vector<int> g[maxn];
bool dfs(int u, int pre, int k, int left, int cnt) {
// cout << "vert: " << u << " | k: " << k << " | left: " << left << " | cnt: " << cnt __ ;
if (left < 0) return 0;
if (k <= 0)
return (cnt == n);
bool ans = 0;
for(auto v : g[u]) if (v != pre) {
maxi(ans, dfs(v, u, k, left - a[v], cnt + 1));
maxi(ans, dfs(v, u, k - 1, x - a[v], cnt + 1));
}
// cout << u _ k _ left _ cnt << " : " << ans __ ;
return ans;
}
void process() {
cin >> n >> x;
FOR(i, 1, n)
cin >> a[i];
FOR(i, 1, n - 1) {
int u, v; cin >> u >> v;
g[u].pb(v);
g[v].pb(u);
}
int l = 0, r = n, ans = -1;
// cout << dfs(1, -1, 3, x - a[1], 1);
while(l <= r) {
int mid = (l + r) >> 1;
if (dfs(1, -1, mid, x - a[1], 1)) {
ans = mid;
r = mid - 1;
} else l = mid + 1;
}
cout << ans;
}
/*-----------------------------*/
______________TgX______________ {
auto start = high_resolution_clock::now();
fastio();
process();
auto stop = high_resolution_clock::now();
auto duration = duration_cast<microseconds>(stop - start);
cerr << "Time: " << duration.count() << " ms" << endl;
}
/*==============================+
|INPUT |
--------------------------------|
================================+
|OUTPUT |
--------------------------------|
===============================*/
