#include <bits/stdc++.h>
#define P pair<int, int>
#define x first
#define y second
using namespace std;
const int MAXN = 2e5 + 50, MAXK = 1e6 + 50;
int n, k, snode, curmx, ans, cnt, size[MAXN], dp[MAXK], mpath[MAXK];
bool chk[MAXN];
vector<P> g[MAXN];
int dfs(int u, int p) {
size[u] = 1;
for(auto v : g[u]) if(!chk[v.x] && v.x != p) {
dfs(v.x, u);
size[u] += size[v.x];
}
return size[u];
}
void findsen(int u, int p, int d) {
int mx = (d - size[u]);
for(auto v : g[u]) if(!chk[v.x] && v.x != p) {
findsen(v.x, u, d);
mx = max(mx, size[v.x]);
}
if(mx < curmx) snode = u, curmx = mx;
}
void dfs1(int u, int p, int cost, int len, bool fill) {
if(cost > k) return;
if(!fill) {
if(dp[k-cost] == cnt && (len + mpath[k-cost] < ans || ans == -1)) ans = len + mpath[k-cost];
if(cost == k && (len < ans || ans == -1)) ans = len;
} else if(dp[cost] < cnt || len < mpath[cost]) dp[cost] = cnt, mpath[cost] = len;
for(auto v : g[u]) if(!chk[v.x] && v.x != p) dfs1(v.x, u, cost + v.y, len + 1, fill);
}
void process(int u) {
++cnt;
if(dfs(u, -1) <= 1) return;
curmx = size[u] + 1;
findsen(u, -1, size[u]);
u = snode;
for(auto v : g[u]) if(!chk[v.x]) dfs1(v.x, snode, v.y, 1, 0), dfs1(v.x, snode, v.y, 1, 1);
chk[u] = true;
for(auto v : g[u]) if(!chk[v.x]) process(v.x);
}
int best_path(int _n, int _k, int h[][2], int l[]) {
n = _n, k = _k;
for(int i = 0; i < n-1; ++i) {
g[h[i][0]].emplace_back(h[i][1], l[i]);
g[h[i][1]].emplace_back(h[i][0], l[i]);
}
cnt = 0;
ans = -1;
process(0);
return ans;
}
