#include<bits/stdc++.h>
using namespace std;
const int maxn = 2e5;
int n, k, ans = 1e9, len[maxn], cnt[maxn];
pair<int, int> road[maxn];
vector<pair<int, int>> adj[maxn];
bool del[maxn];
void DFS_cnt(int u, int p){
cnt[u] = 1;
for (int i = 0; i < adj[u].size(); ++i){
int v = adj[u][i].first;
if (v == p || del[v]) continue;
DFS_cnt(v, u);
cnt[u] += cnt[v];
}
return;
}
int find_centroid(int u, int p, int n){
for (int i = 0; i < adj[u].size(); ++i){
int v = adj[u][i].first;
if (v == p || del[v]) continue;
if (cnt[v] > n / 2)
return find_centroid(v, u, n);
}
return u;
}
void DFS_solve(int u, int p, int dis, int highways, vector<pair<int, int>>& vec){
if (dis > k) return;
vec.push_back({dis, highways});
for (int i = 0; i < adj[u].size(); ++i){
int v = adj[u][i].first, w = adj[u][i].second;
if (del[v] || v == p) continue;
DFS_solve(v, u, dis + w, highways + 1, vec);
}
return;
}
void solve(int u){
DFS_cnt(u, -1);
int centroid = find_centroid(u, -1, cnt[u]);
del[centroid] = true;
map<int, int> mp;
mp[0] = 0;
for (int i = 0; i < adj[centroid].size(); ++i){
int v = adj[centroid][i].first, w = adj[centroid][i].second;
if (del[v]) continue;
vector<pair<int, int>> vec;
DFS_solve(v, centroid, w, 1, vec);
for (int j = 0; j < vec.size(); ++j){
int dis = vec[j].first, num = vec[j].second;
if (mp.find(k - dis) != mp.end()){
ans = min(ans, mp[k - dis] + num);
}
if (mp.find(dis) == mp.end())
mp[dis] = num;
else mp[dis] = min(mp[dis], num);
}
}
for (int i = 0; i < adj[centroid].size(); ++i){
int v = adj[centroid][i].first;
if (!del[v]) solve(v);
}
return;
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
memset(del, false, sizeof(del));
cin >> n >> k;
for (int i = 0; i < n - 1; ++i)
cin >> road[i].first >> road[i].second;
for (int i = 0; i < n - 1; ++i)
cin >> len[i];
for (int i = 0; i < n - 1; ++i){
adj[road[i].first].push_back({road[i].second, len[i]});
adj[road[i].second].push_back({road[i].first, len[i]});
}
solve(0);
if (ans == 1e9) cout << -1;
else cout << ans;
return 0;
}
