#include <bits/stdc++.h>
using namespace std::literals::string_literals;
using i64 = std::int_fast64_t;
using std::cout;
using std::cerr;
using std::endl;
using std::cin;

template<typename T>
std::vector<T> make_v(size_t a){return std::vector<T>(a);}

template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts){
  return std::vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}

int main() {
	int n, k; scanf("%d%d", &n, &k);
	std::vector<int> a(n), b(n);
	std::vector<std::vector<int>> g(n);
	for(int i = 0; i < n - 1; i++) {
		scanf("%d%d", &a[i], &b[i]);
		a[i]--; b[i]--;
		g[a[i]].push_back(i);
		g[b[i]].push_back(i);
	}

	if(n < k) {
		printf("-1\n");
		return 0;
	}

	k--;
	i64 ans = 0;
	std::queue<int> qu({0});
	std::vector<bool> used(n, false); used[0] = true;
	while(!qu.empty() and k) {
		int v = qu.front(); qu.pop();
		
		for(int id: g[v]) {
			int to = a[id] ^ b[id] ^ v;
			if(used[to]) continue; used[to] = true;

			ans++;
			if(!(--k)) break;
			qu.push(to);
		}
	}

	printf("%ld\n", ans);
	return 0;
}