#include<bits/stdc++.h>
#include <cstdio>
using namespace std;
#define N 200005
#define ff first
#define ss second
#define ll long long
#define pb push_back
#define pii pair<ll,ll>
#define mod 1000000007
#define inf 1e18
vector<ll>gr[N];
map<ll, ll>edge[N];
map<ll, ll>m[N];
ll depth[N];
ll fin_ans;
ll val[N];
ll k;
ll dfs(ll node, ll par)
{
ll sz = -1;
ll ind;
ll not_child = 1;
for (auto child : gr[node])
{
if (child != par )
{
not_child = 0;
ll temp = dfs(child, node);
if (temp > sz)
{
sz = temp;
ind = child;
}
}
}
if (not_child == 1) {
val[node] = 0;
depth[node] = 0;
return 0;
}
for (auto child : gr[node])
{
if (child == par)
continue;
ll to_find = k - edge[node][child];
if (to_find == 0)
fin_ans = 1;
to_find = to_find - val[child];
if (m[child].find(to_find) != m[child].end())
{
fin_ans = min(fin_ans, 1 + depth[child] - m[child][to_find]);
}
}
m[node].swap(m[ind]);
depth[node] = depth[ind] + 1;
val[node] = val[ind] + edge[node][ind];
m[node][edge[node][ind] - val[node]] = depth[node] - 1;
m[ind].clear();
////////////////////////////////alll deal with child to node
// and inserted bigger_child and done with that
for (auto child : gr[node])
{
if (child != par && child != ind)
{
for (auto i : m[child])
{
ll num = i.ff + val[child] + edge[node][child];
ll to_find = k - num - val[node];
if (m[node].find(to_find) != m[node].end())
{
fin_ans = min(fin_ans, depth[node] - m[node][to_find] + depth[child] - i.ss + 1);
}
}
ll findd = k - edge[node][child] - val[node];
if (m[node].find(findd) != m[node].end())
{
fin_ans = min(fin_ans, depth[node] - m[node][findd] + 1);
}
for (auto i : m[child])
{
ll num = i.ff + val[child];
ll to_insert = num - val[node];
ll newd = depth[node] - 1 - (depth[child] - i.ss);
if (m[node].find(to_insert) != m[node].end())
{
if (m[node][to_insert] < newd)
m[node][to_insert] = newd;
}
else
m[node][to_insert] = newd;
}
m[node][edge[node][child] - val[node]] = depth[node] - 1;
m[child].clear();
}
}
return m[node].size();
}
int best_path(int n, int K, int H[][2], int L[]) {
ll i, a, b, c;
k = (ll)K;
for (ll i = 0; i <= n; i++)
{
gr[i].clear();
m[i].clear();
depth[i] = 0;
val[i] = 0;
edge[i].clear();
}
fin_ans = inf;
for (i = 0; i < n - 1; i++) {
a = H[i][0]; b = H[i][1]; c = L[i];
a++; b++;
edge[a][b] = c;
edge[b][a] = c;
gr[a].pb(b);
gr[b].pb(a);
}
dfs(1, 0);
if (fin_ans == inf )
return -1;
return (int )fin_ans;
}
