#include <algorithm>
#include <bits/stdc++.h>
#include <functional>
using namespace std;
int n, k;
vector<vector<int>> graph;
vector<vector<pair<int, int>>> child_len;
int mn;
int pull_up(int node, int par) {
for (auto next : graph[node]) {
if (next != par) {
child_len[node].push_back({pull_up(next, node), next});
}
}
sort(child_len[node].begin(), child_len[node].end(), greater<pair<int, int>>());
int mx = 0;
if (child_len[node].size()) {
mx = child_len[node][0].first;
}
return mx + 1;
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n >> k;
graph.resize(n); child_len.resize(n);
for (int i = 0; i < n - 1; i++) {
int a, b;
cin >> a >> b;
graph[--a].push_back(--b);
graph[b].push_back(a);
}
mn = 2 * n - 2;
pull_up(0, -1);
if (k == 1) {
for (int i = 0; i < n; i++) {
if (child_len[i].size() > 1) {
mn = min(mn, 2 * n - 2 - child_len[i][0].first - child_len[i][1].first);
} else if (child_len[i].size()) {
mn = min(mn, 2 * n - 2 - child_len[i][0].first + 1);
}
}
cout << mn << "\n";
} else {
cout << "-1";
}
}
