#include <bits/stdc++.h>
using namespace std;
const int MAXN = 200010;
const int MAXK = 1000010;
const int M = 2 * MAXN;
const int inf = 0x3f3f3f3f;
int hd[MAXN], nx[M], to[M], wt[M], ei = 0;
inline void link(int i, int j, int kk) {
nx[++ei] = hd[i], wt[ei] = kk, hd[i] = ei, to[ei] = j;
}
int n, k, ss[MAXN], dep, cc[MAXK], ans;
bool vv[MAXN];
int subtree(int x, int p = 0) {
ss[x] = 1;
for (int j = hd[x], y; j; j = nx[j])
if (!vv[y = to[j]] && y != p)
ss[x] += subtree(y, x);
return ss[x];
}
int centroid(int dd, int x, int p = 0) {
for (int j = hd[x], y; j; j = nx[j])
if (!vv[y = to[j]] && y != p && ss[y] > dd)
return centroid(dd, y, x);
return x;
}
void _fill(int x, int p, int w, int d) {
if (w > k) return;
cc[w] = min(cc[w], d);
dep = max(dep, w);
for (int j = hd[x], y; j; j = nx[j])
if (!vv[y = to[j]] && y != p)
_fill(y, x, w + wt[j], d + 1);
}
void _count(int x, int p, int w, int d) {
if (w > k) return;
ans = min(ans, d + cc[k - w]);
for (int j = hd[x], y; j; j = nx[j])
if (!vv[y = to[j]] && y != p)
_count(y, x, w + wt[j], d + 1);
}
void decomp(int x = 1) {
int c = centroid(subtree(x) / 2, x);
dep = 0, vv[c] = 1;
for (int j = hd[c], y; j; j = nx[j])
if (!vv[y = to[j]]) {
_count(y, c, wt[j], 1);
_fill(y, c, wt[j], 1);
}
for (int i = 1; i <= dep; ++i) cc[i] = inf;
for (int j = hd[c], y; j; j = nx[j])
if (!vv[y = to[j]])
decomp(y);
}
int best_path(int N, int K, int H[][2], int L[]){
n = N, k = K;
memset(vv, 0, sizeof(vv));
memset(hd, 0, sizeof(hd));
ans = inf, ei = 0;
for (int i = 0; i + 1 < n; ++i) {
++H[i][0], ++H[i][1];
link(H[i][0], H[i][1], L[i]);
link(H[i][1], H[i][0], L[i]);
}
memset(cc, 0x3f, sizeof(cc)); cc[0] = 0;
decomp();
return (ans == inf ? -1 : ans);
}
/**
int main() {
scanf("%d%d", &n, &k);
memset(vv, 0, sizeof(vv));
memset(hd, 0, sizeof(hd));
ans = inf, ei = 0;
for (int i = 1, x, y, z; i < n; ++i) {
scanf("%d%d%d", &x, &y, &z); ++x, ++y;
link(x, y, z), link(y, x, z);
}
memset(cc, 0x3f, sizeof(cc)); cc[0] = 0;
decomp();
printf("%d\n", (ans == inf ? -1 : ans));
}
**/
