// By AmmarDab3an - Aleppo University
#include "bits/stdc++.h"
using namespace std;
// #define int int64_t
// #define ll int64_t
typedef unsigned int uint;
typedef long long int ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> iii;
typedef pair<ll, pll> lll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<pii> vpii;
typedef vector<pll> vpll;
#define endl '\n'
#define fastIO ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define freopenI freopen("input.txt", "r", stdin);
#define freopenO freopen("output.txt", "w", stdout);
const int INF = 0x3f3f3f3f;
const ll INFLL = 0x3f3f3f3f3f3f3f3f;
const int MOD = 1e9 + 7;
const double EPS = 1e-9;
const double PI = acos(-1);
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int rand(int x, int y) {
return uniform_int_distribution<int>(x, y)(rng);
}
int mul(int a, int b){
int ret = (1ll * (a%MOD) * (b%MOD)) % MOD;
return (ret+MOD)%MOD;
}
int add(int a, int b){
int ret = (1ll * (a%MOD) + (b%MOD)) % MOD;
return (ret+MOD)%MOD;
}
int pow_exp(int n, int p){
if(!p) return 1;
if(p&1) return mul(n, pow_exp(n, p-1));
int tmp = pow_exp(n, p/2);
return mul(tmp, tmp);
}
const int NMAX = 2e5 + 10;
const int LOG_MAX = ceil(log2(double(NMAX)));
int n, k, log_n;
vpii adj[NMAX];
int depth[NMAX], sub[NMAX], par[NMAX][LOG_MAX];
int cpar[NMAX];
void dfs0(int u, int p){
for(auto [v, w]: adj[u]) if(v != p){
depth[v] = depth[u] + 1;
par[v][0] = u;
for(int i = 1; i < log_n; i++)
par[v][i] = par[par[v][i-1]][i-1];
dfs0(v, u);
}
}
int lca(int u, int v){
if(depth[u] < depth[v]) swap(u, v);
int diff = depth[u] - depth[v];
for(int i = 0; i < log_n; i++) if(diff & (1<<i)) u = par[u][i];
if(u == v) return u;
for(int i = log_n-1; i >= 0; i--) if(par[u][i] != par[v][i])
u = par[u][i], v = par[v][i];
return par[u][0];
}
int dist(int u, int v){
return depth[u] + depth[v] - 2 * depth[lca(u, v)];
}
int nn;
void dfs1(int u, int p){
nn++;
sub[u] = 1;
for(auto [v, w] : adj[u]) if(v != p){
dfs1(v, u);
sub[u] += sub[v];
}
}
int dfs2(int u, int p){
for(auto [v, w] : adj[u]) if(v != p) if(sub[v] > nn/2){
return dfs2(v, u);
}
return u;
}
int _dist[NMAX];
int _depth[NMAX];
map<int, int> freq;
vi update_later;
int go(int u, int p){
int ret = INF;
auto it = freq.find(k-_dist[u]);
if(it != freq.end()){
ret = it->second + _depth[u];
}
update_later.push_back(u);
for(auto [v, w] : adj[u]) if(v != p){
_dist[v] = _dist[u]+w;
_depth[v] = _depth[u]+1;
ret = min(ret, go(v, u));
if(p==-1){
for(auto u : update_later){
auto it = freq.find(_dist[u]);
if(it==freq.end()){
freq[_dist[u]] = _depth[u];
}
else{
freq[_dist[u]] = min(it->second, _depth[u]);
}
}
update_later.clear();
}
}
return ret;
}
int decompose(int u, int p){
nn = 0;
dfs1(u, u);
int centroid = dfs2(u, u);
if(p == -1) p = centroid;
cpar[centroid] = p;
_dist[centroid] = 0;
_depth[centroid] = 0;
update_later.clear();
freq.clear();
int ret = go(centroid, -1);
for(auto [v, w] : adj[centroid]){
adj[v].erase(find(adj[v].begin(), adj[v].end(), (pii){centroid, w}));
ret = min(ret, decompose(v, centroid));
}
adj[centroid].clear();
return ret;
}
int best_path(int32_t N, int32_t K, int32_t H[][2], int32_t L[]){
::n = N;
::k = K;
log_n = ceil(log2(double(N)));
for(int i = 0; i < n; i++){
adj[i].clear();
}
for(int i = 0; i < n-1; i++){
int u = H[i][0];
int v = H[i][1];
adj[u].push_back({v, L[i]});
adj[v].push_back({u, L[i]});
}
dfs0(0, -1);
int ret = decompose(0, -1);
if(ret==INF) ret = -1;
return ret;
}
#ifdef CPEDU
int32_t main(){
fastIO;
#ifdef LOCAL
freopenI;
freopenO;
#endif
// freopen("name.in", "r", stdin);
int N, K;
cin >> N >> K;
int H[N-1][2];
for(int i = 0; i < N-1; i++){
cin >> H[i][0] >> H[i][1];
}
int L[N-1];
for(int i = 0; i < N-1; i++){
cin >> L[i];
}
cout << best_path(N, K, H, L) << endl;
}
#endif
