#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ld double
const int INF = 1e18;
const int mod = 12345;
const int sz = 1e6 + 5;
int n , k , dp[sz];
vector < vector < int > > adj;
vector < bool > vis(sz , false);
int ans = 0 , sum = 0 , summ = 0;
void dfs(int v){
vis[v] = 1;
summ += dp[v];
sum += dp[v];
if(sum > k){
ans++;
sum = dp[v];
}
for(int u : adj[v]){
if(!vis[u])
dfs(u);
}
}
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> n >> k;
adj.resize(n + 1);
for(int i = 1;i <= n;i++) cin >> dp[i];
int u[n] , v[n];
for(int i = 0;i < n - 1;i++){
cin >> u[i] >> v[i];
adj[u[i]].push_back(v[i]);
adj[v[i]].push_back(u[i]);
}
if(n <= 15)
{
int cav = INF;
for(int bit = 0;bit < pow(2 , n) - 1;bit++){
vis.assign(sz , false);
adj.clear();
adj.resize(n + 1);
int cnt = 0;
for(int i = 0;i < n - 1;i++){
if((1 << i) & bit){
adj[u[i]].push_back(v[i]);
adj[v[i]].push_back(u[i]);
}
else{
cnt++;
}
}
int tot[2];
tot[0] = tot[1] = 0;
for(int i = 1;i <= n;i++){
if(!vis[i]){
tot[0]++;
dfs(i);
if(k >= summ) tot[1]++;
summ = 0;
}
}
if(tot[1] == tot[0]){
cav = min(cav , cnt);
}
}
cout << cav << endl;
return 0;
}
adj.clear();
for(int i = 0;i < n - 1;i++){
cin >> u[i] >> v[i];
adj[u[i]].push_back(v[i]);
adj[v[i]].push_back(u[i]);
}
dfs(1);
cout << ans << endl;
}
