#include <bits/stdc++.h>
using namespace std;
const int inf=1001001001;
int n,i,x,y,z,l,r,h,s[100100];
long long m,cnt;
vector<int> g[100100],f[100100];
void dfs(int i, int p, int d, int e, int w) {
  for (s[d]=w; e<d && s[d]-s[e]>h; e++);
  cnt+=d-e;
  for (int j=0; j<g[i].size(); j++) {
    int k=g[i][j];
    if (k==p) continue;
    dfs(k,i,d+1,e,w+f[i][j]);
  }
}
int main() {
  cin>>n>>m;
  for (i=1; i<n; i++) {
    scanf("%d%d%d",&x,&y,&z);
    g[x].push_back(y); f[x].push_back(z);
    g[y].push_back(x); f[y].push_back(z);
  }
  l=1; r=inf;
  while (l<r) {
    h=(l+r)/2;
    cnt=0;
    dfs(1,0,0,0,0);
    if (cnt>=m) r=h; else l=h+1;
  }
  printf("%d\n",r==inf?-1:r);
  return 0;
}