#include <algorithm>
#include <cmath>
#include <iostream>
#include <deque>
#include <vector>
#include <string>
#include <utility>
#include <queue>
#include <unordered_map>
#include <unordered_set>

using namespace std;

int main()
{
	int n, k;
	cin >> n >> k;

	if (k > n)
	{
		cout << -1 << endl;
		return 0;
	}

	vector<unordered_set<int>> edges(n);

	for (int i = 0; i < n - 1; ++i)
	{
		int a, b;
		cin >> a >> b;
		edges.at(a - 1).emplace(b - 1);
		edges.at(b - 1).emplace(a - 1);
	}

	deque<int> searchingNode;
	for (int node : edges.at(0))
	{
		searchingNode.emplace_back(node);
	}

	deque<int> nextCandidateNode;

	unordered_set<int> reachedNode;
	reachedNode.emplace(0);

	int depth = 0;
	long long result = 0;

	while (k > 1)
	{
		++depth;
		for (int node : searchingNode)
		{
			--k;
			++result;

			if( k <= 1)
			{
				break;
			}

			for (int nextNode : edges.at(node))
			{
				if (reachedNode.find(nextNode) == reachedNode.end())
				{
					nextCandidateNode.emplace_back(nextNode);
					reachedNode.emplace(nextNode);
				}
			}
		}
		searchingNode.clear();
		swap(searchingNode, nextCandidateNode);
	}
	cout << result << endl;
}