#pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define int long long
#define pb push_back
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define endl "\n"
#define Yes cout << "YES" << endl;
#define No cout << "NO" << endl;
#define mod(a) ((a % MOD + MOD) % MOD)
#define inp(v) for(auto &a : v) cin >> a;
#define out(v) for(auto &a : v) cout << a << " ";
const int MOD = (int)1e9 + 7;
const int MAX = (int)1e5 + 5;
vector<int> adj[MAX];
void solve() {
//x >> y = x / (2 ^ y)
//x << y = x * (2 ^ y)
int n;
cin >> n;
int k;
cin >> k;
int h[n + 1];
for(int i = 1; i <= n; i++) {
cin >> h[i];
}
for(int i = 1; i < n; i++) {
int x,y;
cin >> x >> y;
adj[x].pb(y);
adj[y].pb(x);
}
multiset<int> st;
int say = 0;
int cem = 0;
for(int i = 1; i <= n; i++) {
cem += h[i];
if(cem > k) {
cem = h[i];
say++;
}
}
cout << say << endl;
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int t = 1;
//cin >> t;
while (t--) {
solve();
}
}
