#include <bits/stdc++.h>
using namespace std;
const long long mod = 1000000007;
const double eps = 1e-9;
const double pi = acos(0) * 2;
long long powmod(long long a, long long b) {
  long long res = 1;
  for (; b; b >>= 1) {
    if (b & 1) res = res * a % mod;
    a = a * a % mod;
  }
  return res;
}
long long powmod(long long a, long long b, long long mod) {
  long long res = 1;
  for (; b; b >>= 1) {
    if (b & 1) res = res * a % mod;
    a = a * a % mod;
  }
  return res;
}
const int N = 201000;
set<int> mp;
int dep[N], f[N], F[N][20], id[N], cnt[N];
int y[N], nxt[N], fst[N], tot, ans, n, k, u, v;
void add(int u, int v) {
  tot++;
  y[tot] = v;
  nxt[tot] = fst[u];
  fst[u] = tot;
}
void dfs(int u, int p) {
  f[u] = p;
  id[cnt[u] = ++tot] = u;
  for (int j = fst[u]; j; j = nxt[j])
    if (y[j] != p) dep[y[j]] = dep[u] + 1, dfs(y[j], u);
}
int LCA(int u, int v) {
  if (dep[u] > dep[v]) swap(u, v);
  for (int k = dep[v] - dep[u], j = 17; j >= 0; j--)
    if ((k >> j) & 1) v = F[v][j], k ^= (1 << j);
  if (u == v) return u;
  for (int k = 17; f[u] != f[v]; u = F[u][k], v = F[v][k])
    for (; k && F[u][k] == F[v][k]; k--)
      ;
  return f[u];
}
void modify(char ch, int u) {
  typeof(mp.begin()) it = mp.lower_bound(cnt[u]);
  if (*it == cnt[u]) mp.erase(cnt[u]), it = mp.lower_bound(cnt[u]);
  if (!mp.size()) {
    if (ch == '+') mp.insert(cnt[u]);
    return;
  }
  int q = id[(it == mp.end()) ? *mp.begin() : *it],
      p = id[(it-- == mp.begin()) ? *(--mp.end()) : *it];
  int dt = dep[u] - dep[LCA(p, u)] - dep[LCA(q, u)] + dep[LCA(p, q)];
  if (ch == '+')
    ans += dt, mp.insert(cnt[u]);
  else
    ans -= dt;
}
bool check(int v) {
  ans = 0;
  mp.clear();
  for (int i = 1; i < (int)v; i++) modify('+', i);
  for (int i = v; i < (int)n + 1; i++) {
    modify('+', i);
    if (ans + 1 <= k) return 1;
    modify('-', i + 1 - v);
  }
  return 0;
}
int main() {
  scanf("%d%d", &n, &k);
  for (int i = 1; i < (int)n; i++) scanf("%d%d", &u, &v), add(u, v), add(v, u);
  tot = 0;
  dfs(1, 0);
  id[n + 1] = n + 1;
  for (int i = 1; i < (int)n + 1; i++) F[i][0] = f[i];
  for (int j = 1; j < (int)18; j++)
    for (int i = 1; i < (int)n + 1; i++)
      F[i + 1][j] = F[F[i + 1][j - 1]][j - 1];
  int l = 1, r = n + 1;
  while (l + 1 < r) {
    int md = (l + r) >> 1;
    if (check(md))
      l = md;
    else
      r = md;
  }
  printf("%d\n", l);
  return 0;
}
