#include <bits/stdc++.h>
#define ll long long
#define all(lpv) lpv.begin(), lpv.end()
#define pot(x, y) lower_bound(x.begin(), x.end(), y) - x.begin() + 1
using namespace std;
//#define lpv
#ifndef lpv
#include "race.h"
#endif // lpv
#define int long long
const int N = 1e6 + 5;
int ans, n, k, d[N], dp[N], sum, cent, sub[N];
vector<pair<int,int>> p[N];
bool del[N];
const int oo = 1e9;
void pre(int u,int v) {
sub[u] = 1;
sum++;
for(auto ptr : p[u]) {
int j, w; tie(j, w) = ptr;
if(j == v || del[j]) continue;
pre(j, u);
sub[u] += sub[j];
}
}
int FIND(int u,int v) {
for(auto ptr : p[u]) {
int j, w; tie(j, w) = ptr;
if(del[j] || j == v) continue;
if(sub[j] > sum / 2) return FIND(j, u);
}
return u;
}
vector<int> collect;
vector<pair<int,int>> vr;
void sol(int u,int v, int edge) {
if(d[u] > k) return;
collect.push_back(d[u]);
vr.push_back({d[u], edge});
ans = min(ans, edge + dp[k - d[u]]);
// cerr << u << " " << v << " " << edge << " " << d[u] << " " << dp[k - d[u]] << " t\n";
for(auto ptr : p[u]) {
int j, w; tie(j, w) = ptr;
if(j == v || del[j]) continue;
d[j] = d[u] + w;
sol(j, u, edge + 1);
}
}
void cen(int u) {
sum = 0;
pre(u, 0);
cent = FIND(u, 0);
del[cent] = 1;
d[cent] = 0;
dp[0] = 0;
collect.clear();
collect.push_back(0);
for(auto ptr : p[cent]) {
int j, w; tie(j, w) = ptr;
if(del[j]) continue;
vr.clear();
d[j] = d[cent] + w;
sol(j, u, 1);
for(auto tmp : vr) {
int x, y; tie(x, y) = tmp;
dp[x] = min(dp[x], y);
}
}
// cerr << cent << " t\n";
// for(auto j : collect) cerr << j << " ";
// cerr << "\n";
for(auto j : collect) dp[j] = oo;
for(auto ptr : p[cent]) {
int j, w; tie(j, w) = ptr;
if(del[j]) continue;
cen(j);
}
}
void dfs(int u,int v,int edge,int wet) {
if(wet == k) ans = min(ans, edge);
for(auto ptr : p[u]) {
int j, w; tie(j, w) = ptr;
if(j == v) continue;
dfs(j, u, edge + 1, wet + w);
}
}
int best_path(int _n, int _k, int H[][2], int L[]) {
n = _n, k = _k;
ans = n;
for(int i = 1; i < n; i ++) {
int x = H[i - 1][0] + 1, y = H[i - 1][1] + 1, c = L[i - 1];
// cerr << x << " " << y << " " << c << " f\n";
p[x].push_back({y, c});
p[y].push_back({x, c});
}
if(n <= 1000) for(int i = 1;i <= n; i ++) dfs(i, 0, 0, 0);
else {
for(int i = 0; i <= k; i ++) dp[i] = oo;
cen(1);
}
// cerr << ans << " result\n";
return (ans == n ? -1 : ans);
}
#ifdef lpv
int h[N][2], l[N];
signed main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define task "v"
if(fopen(task ".inp","r")) {
freopen(task ".inp","r",stdin);
freopen(task ".out","w",stdout);
}
int _n, _k; cin >> _n >> _k;
for(int i = 1; i < _n; i ++) {
cin >> h[i - 1][0] >> h[i - 1][1] >> l[i - 1];
}
cout << best_path(_n, _k, h, l);
}
#endif // lpv
