#include<bits/stdc++.h>
using namespace std;
#define il inline 
typedef long long ll;
#define re register
const int N=50005;
int n,m; 
int hed[N],tal[N<<1],nxt[N<<1],cnt=0;
ll val[N<<1];
ll l=1,r=0,mid;
ll ans=-1;
ll dis[N];
int sum;
il ll llmax(ll x,ll y){
    return x>y?x:y;
}
il void addege(int x,int y,ll z){
    cnt++;
    tal[cnt]=y;
    val[cnt]=z;
    nxt[cnt]=hed[x];
    hed[x]=cnt;
}
il ll dfs(int u,int fa){
    multiset<ll> s;
    for(re int i=hed[u];i;i=nxt[i]){
        int v=tal[i];
        if(v==fa) continue;
        ll value=val[i]+dfs(v,u);
        if(value>=mid){
            sum++;
        }
        else{
            s.insert(value);
        }
    }
    ll l=0;
    while(!s.empty()){
        ll p=*s.begin();
        s.erase(s.begin());
        multiset<ll>::iterator it=s.lower_bound(mid-p);
        if(it!=s.end()){
            s.erase(it);
            sum++;
        }
        else{
            l=llmax(l,p);
        }
    }
    return l;
}
il bool check(){
    sum=0;
    dfs(1,1);
    return sum>=m;
}
il void Dfs(int u,int fa){
    for(re int i=hed[u];i;i=nxt[i]){
        int v=tal[i];
        if(v==fa) continue;
        dis[v]=dis[u]+val[i];
        Dfs(v,u);
    }
}
il void cal(){
    memset(dis,0,sizeof(dis));
    int pos=1;
    Dfs(pos,pos);
    for(re int i=2;i<=n;i++){
        if(dis[i]>dis[pos]) pos=i;
    }
    memset(dis,0,sizeof(dis));
    Dfs(pos,pos);
    for(re int i=1;i<=n;i++){
        if(dis[i]>dis[pos]) pos=i;
    }
    r=dis[pos];
    //cout<<r<<endl;
}
int main(){
    scanf("%d%d",&n,&m);
    for(re int i=1;i<n;i++){
        int x,y;
        ll z;
        scanf("%d%d%lld",&x,&y,&z);
        addege(x,y,z);
        addege(y,x,z); 
    } 
    cal();
    while(l<=r){
        mid=(l+r)/2ll;
        if(check()) ans=mid,l=mid+1;
        else r=mid-1;
    }
    printf("%lld\n",ans);
    return 0;
}