#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
#define mp make_pair
#define pb push_back
#define F first
#define S second
#define debug(x) std::cout << #x << ": " << x << "\n"
#define all(v) v.begin(), v.end()
#define li(i,a,b) for (int (i) = (a); (i) < (b); (i)++)
#define endl '\n'
#define mem(name,val) memset(name,val,sizeof(name))
#define min(a,b) (a<=b ? a : b)
#define max(a,b) (a>=b ? a : b)
//using u64 = uint64_t;
//using u128 = __uint128_t;
const int nmax = 2e5+3;
const int kmax = 1e6+3;
vector<pii> adj[nmax];
int ans=-1, K, sz[nmax], r[nmax], bes[kmax];
int dfs_sz(int u, int p=-1){
sz[u]=1;
for(auto [v,_]:adj[u]){
if(p==v||r[v])continue;
sz[u]+=dfs_sz(v,u);
}
return sz[u];
}
int get_cent(int u, int ts, int p=-1){
for(auto [v,_] : adj[u]){
if(p==v||r[v])continue;
if(sz[v]*2>ts)return get_cent(v,ts,u);
}
return u;
}
void minimize(int &a, int b){
if(a==-1 || a > b){
a = b;
}
}
void slv_cent(int u, int p, int sum, int cnt, bool sw){
if(sum>K) return;
if(sw){
if(bes[K-sum]!=-1)
minimize(ans,bes[K-sum]+cnt);
}
else{
minimize(bes[sum], cnt);
}
for(auto [v,len]: adj[u]){
if(p==v || r[v]) continue;
slv_cent(v,u,sum+len,cnt+1,sw);
}
}
void del(int u, int p, int sum){
if(sum>K)return;
bes[sum]=-1;
for(auto [v,len]:adj[u]){
if(p==v||r[v])continue;
del(v,u,len+sum);
}
}
void solve(int u){
u = get_cent(u,dfs_sz(u));
r[u]=1;
bes[0]=0;
for(auto [v,len] : adj[u]){
if(r[v]) continue;
slv_cent(v,u,len,1,true);
slv_cent(v,u,len,1,false);
}
//clear
for(auto [v,len] : adj[u]){
if(r[v]) continue;
del(v,u,len);
}
for(auto [v,_] : adj[u]){
if(!r[v]) solve(v);
}
}
int best_path(int n, int k, int h[][2], int l[]){
K=k;
li(i,0,n-1){
adj[h[i][0]].pb({h[i][1],l[i]});
adj[h[i][1]].pb({h[i][0],l[i]});
}
mem(r,0);
mem(bes,-1);
solve(0);
return ans;
}
