#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 10, M = 1e6+10;
vector< pair<int, int> > G[N];
int n, k;
int siz[N], all, rt, rtmaxsiz;
int dis1[N], dis2[N], cnt, ans, mi[M];
bool del[N];

void getroot(int x, int xfa)
{
    siz[x] = 1;
    int xmaxsiz = 0;
    for (auto i:G[x])
        if (i.first != xfa && !del[i.first]){
            getroot(i.first, x);
            siz[x] += siz[i.first];
            xmaxsiz = max(xmaxsiz, siz[i.first]);
        }
    xmaxsiz = max(xmaxsiz, all - siz[x]);
    if (xmaxsiz < rtmaxsiz) rtmaxsiz = xmaxsiz, rt = x;
}

void getdis(int x, int xfa, int d1, int d2)
{
    if(d1>k) return;
    dis1[++cnt]=d1; dis2[cnt]=d2;
    for (auto i:G[x])
        if (i.first != xfa && !del[i.first])
            getdis(i.first, x, d1+i.second, d2+1);
}

void calc(int x)
{
    mi[0]=0; cnt=0;
    for(auto i:G[x])
        if(!del[i.first]){
            int oldcnt=cnt;getdis(i.first, x, i.second, 1);
            for(int j=oldcnt+1;j<=cnt;j++) ans=min(ans,mi[k-dis1[j]]+dis2[j]);
            for(int j=oldcnt+1;j<=cnt;j++) mi[dis1[j]]=min(mi[dis1[j]],dis2[j]);
        }
    for(int i=1;i<=cnt;i++) mi[dis1[i]]=0x3f3f3f3f;
}
void divide(int x)
{
    del[x] = true;
    calc(x);
    for (auto i:G[x])
        if (!del[i.first]){
            all=rtmaxsiz=siz[i.first];getroot(i.first, x);getroot(rt, x);
            divide(rt);
        }
}
int main()
{
    ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    cin >> n >>k;
    for(int i=1;i<=n;i++) G[i].clear();
    for (int i = 1, x, y, w; i < n; i++)
    {
        cin >> x >> y >> w;x++;y++;
        G[x].push_back({y, w});
        G[y].push_back({x, w});
    }
    all=rtmaxsiz=n;getroot(1, 0);getroot(rt,0);
    memset(mi,0x3f,sizeof mi);memset(del,0,sizeof del);
    ans = n;divide(rt);
    if(ans>=n) cout << -1 ; else  cout <<  ans ;
    return 0;
}