#include "bits/stdc++.h"
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define ll long long
#define pb push_back
#define in insert
#define F first
#define S second
#define vll vector<ll>
#define all(v) v.begin(),v.end()
#define endl '\n'
#define pii pair<ll,ll>
using namespace std;
const ll INF =1e18, mod = 1e9 + 7, N = 1e5 + 5;
ll gcd(ll a, ll b){
if(b == 0){
return a;
}
return gcd(b, a % b);
}
ll lcm(ll a, ll b){
return (a / gcd(a,b)) * b;
}
vector<ll>g[N];
ll used[N];
ll sum = 0;
ll n,k;
ll a[N];
ll cnt = 0;
void dfs(ll s){
used[s] = 1;
for(auto i : g[s]){
if(!used[i]){
if(a[i] + sum <= k){
sum += a[i];
}
else{
cnt++;
sum = a[i];
}
dfs(i);
}
}
}
void solve(){
cin >> n >> k;
for(int i = 1; i <= n; i++){
cin >> a[i];
}
ll x,y;
for(int i = 0; i < n - 1; i++){
cin >> x >> y;
g[x].pb(y);
g[y].pb(x);
}
ll mini = INT_MAX;
for(int i = 1; i <= n; i++){
sum = a[i];
cnt = 0;
for(int i =1; i <= n; i++){
used[i] = 0;
}
dfs(i);
mini = min(mini, cnt);
}
cout << mini <<endl;
}
int main(){
fast;
ll t = 1;
// cin >> t;
while(t--){
solve();
}
return 0;
}
