#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main() {
    int N, K;
    cin >> N >> K;
    vector<int> adj[N];
    for (int i = 0; i < N - 1; i++) {
        int a, b;
        cin >> a >> b;
        adj[a - 1].push_back(b - 1);
        adj[b - 1].push_back(a - 1);
    }
    deque<int> q;
    q.push_back(0);
    int cnt = 0;
    bool vis[N]{};
    vis[0] = true;
    while (!q.empty()) {
        int v = q.front();
        q.pop_front();
        for (int u : adj[v]) {
            if (vis[u]) continue;
            vis[u] = true;
            cnt++;
            q.push_back(u);
        }
    }
    if (cnt >= K - 1) {
        cout << K - 1 << "\n";
    } else {
        cout << "-1\n";
    }
    return 0;
}