#include <bits/stdc++.h>
using namespace std;
const int M = 1e5 + 1;
vector<int> nei[M];
int cts[M],sps[M],k;
void dfs(int u,int p=0)
{
vector<int> v;
for (int i:nei[u])
if (i!=p)
{
dfs(i,u);
cts[u]+=cts[i];
sps[u]+=sps[i];
v.push_back(sps[i]);
}
sort(v.begin(),v.end());
while (sps[u]>k)
{
sps[u]-=v.back();
cts[u]++;
}
}
int main()
{
int n;
cin>>n>>k;
int a[n];
for (int i=1;i<=n;i++)
cin>>a[i];
for (int i=1;i<n;i++)
{
int u,v;
cin>>u>>v;
nei[u].push_back(v);
nei[v].push_back(u);
}
int ans=n-1;
for (int i=1;i<=n;i++)
{
for (int j=1;j<=n;j++)
sps[j]=a[j],cts[j]=0;
dfs(i);
ans=min(ans,cts[i]);
}
cout<<ans<<endl;
return 0;
}
