#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 = 3e6 + 5;
int n , k , dp[sz];
vector < vector < int > > adj;
vector < bool > vis(sz , false);
int ans = 0 , sum = 0;
void dfs(int v){
vis[v] = 1;
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]);
}
dfs(1);
cout << ans << endl;
}
