#include <bits/stdc++.h>
using namespace std;
template <typename A, typename B, typename C>
struct triple {
  A X;
  B Y;
  C Z;
  triple(A a = 0, B b = 0, C c = 0) : X(a), Y(b), Z(c) {}
};
template <typename A, typename B, typename C>
triple<A, B, C> make_triple(A a = 0, B b = 0, C c = 0) {
  return triple<A, B, C>(a, b, c);
}
template <typename A, typename B, typename C>
bool operator<(const triple<A, B, C>& a, const triple<A, B, C>& b) {
  if (a.X != b.X) return a.X < b.X;
  if (a.Y != b.Y) return a.Y < b.Y;
  return a.Z < b.Z;
}
template <typename T, typename SS>
ostream& operator<<(ostream& ofs, const pair<T, SS>& p) {
  ofs << "( " << p.first << " , " << p.second << " )";
  return ofs;
}
template <typename T>
void print(T a) {
  for (auto i : a) cout << i << ' ';
  cout << '\n';
}
template <typename T>
T max(T a, T b, T c) {
  return max(a, max(b, c));
}
template <typename T>
T min(T a, T b, T c) {
  return min(a, min(b, c));
}
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }
  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
signed main() {
  srand(time(NULL));
  cin.tie(0);
  cout.tie(0);
  ios_base::sync_with_stdio(false);
  long long n, k;
  cin >> n >> k;
  if (n == 1) return cout << "0\n", 0;
  vector<vector<pair<long long, long long> > > g(n);
  map<long long, map<long long, long long> > dp;
  for (long long _ = 0; _ < (n - 1); _++) {
    long long x, y, z;
    cin >> x >> y >> z;
    x--, y--;
    dp[x][y] = dp[y][x] = z;
    g[x].push_back(make_pair(y, z));
    g[y].push_back(make_pair(x, z));
  }
  function<long long(long long)> d = [&](long long s) {
    vector<long long> h(n);
    function<void(long long, long long, long long)> dfs =
        [&](long long v, long long p, long long hh) {
          h[v] = hh;
          for (auto to : g[v])
            if (to.first != p) dfs(to.first, v, hh + to.second);
        };
    dfs(s, -1, 0);
    return max_element(h.begin(), h.end()) - h.begin();
  };
  long long x = d(0);
  long long y = d(x);
  vector<long long> p(n);
  function<void(long long, long long)> dfs = [&](long long v, long long pp) {
    p[v] = pp;
    for (auto to : g[v])
      if (to.first != pp) dfs(to.first, v);
  };
  dfs(x, -1);
  deque<long long> path;
  path.push_back(y);
  while (p[y] != x) {
    y = p[y];
    path.push_back(y);
  }
  path.push_back(x);
  long long d1 = 0, d2 = 0;
  while (path.size() > k + 2) {
    if (d1 < d2) {
      d1 += dp[path.front()][path[1]];
      path.pop_front();
    } else {
      d2 += dp[path.back()][path[path.size() - 2]];
      path.pop_back();
    }
  }
  auto solve = [&](deque<long long> use) -> long long {
    vector<long long> used(n);
    for (auto i : use) used[i] = 1;
    function<long long(long long, long long, long long)> dfs =
        [&](long long v, long long p, long long hh) {
          long long ans = hh;
          for (auto to : g[v])
            if (to.first != p && !used[to.first])
              ans = max(ans, dfs(to.first, v, hh + to.second));
          return ans;
        };
    long long ans = 0;
    for (auto i : use) ans = max(ans, dfs(i, -1, 0));
    return ans;
  };
  long long ans = 1e17;
  if (path.size() == k + 2) {
    long long xx = path.front();
    long long xx2 = path[1];
    path.pop_front();
    path.pop_front();
    ans = min(ans, solve(path));
    path.push_front(xx2);
    path.push_front(xx);
    xx = path.back();
    xx2 = path[path.size() - 2];
    path.pop_back();
    path.pop_back();
    ans = min(ans, solve(path));
    path.push_back(xx2);
    path.push_back(xx);
    path.pop_front();
    path.pop_back();
    ans = min(ans, solve(path));
  } else if (path.size() == k + 1) {
    long long xx = path.front();
    path.pop_front();
    ans = min(ans, solve(path));
    path.push_front(xx);
    xx = path.back();
    path.pop_back();
    ans = min(ans, solve(path));
  } else
    ans = min(ans, solve(path));
  cout << ans << '\n';
}
