import java.util.*;
public class Main {

  public static void main(String[] args) { 
      Scanner sc = new Scanner(System.in);
      int n = sc.nextInt();
      int k = sc.nextInt();
      Map<Integer, List<Integer>> graph = new HashMap<>();
      for(int i = 1; i <= n; i++)
        graph.put(i, new ArrayList<>());

      for(int i = 0; i < n-1; i++) {
        int a = sc.nextInt();
        int b = sc.nextInt();
        graph.get(a).add(b);
        graph.get(b).add(a);
      }
      Queue<Integer> queue = new LinkedList<>();
      queue.offer(1);
      Set<Integer> visited = new HashSet<>();
      visited.add(1);
      k--;
      int steps = 0;
      if(k == 0) {
        System.out.println(steps);
        return;
      }
      while(!queue.isEmpty()) {
        int node = queue.poll();
        List<Integer> adj = graph.get(node);
        for(int adjNode : adj) {
          if(visited.contains(adjNode)) continue;
          visited.add(adjNode);
          queue.offer(adjNode);
          k--;
          steps++;
          if(k == 0) {
            System.out.println(steps);
            return;
          }
        }
      }
      System.out.println(-1);
  }
}