#include<iostream>
#include<vector>
#include<algorithm>
#include<map>
#include<cstring>
#include<math.h>
#include<bitset>
#include<queue>
#include<set>
#include<iomanip>
#include<assert.h>
#include<string>
#include<cstdlib>
#include<cctype>
#include<unordered_map>
#include<sstream>
#include<numeric>
#include<stack>
// #include<bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int,int>;
constexpr ll INF = 9e18;
constexpr int inf = 1e9;
const double INFD = 1e100;
const ll mod = 1000000007;
const double PI = 3.1415926535897932384626433832795028841971;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
};
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
};

// intやllをstringに変換
template<typename T> inline string toString(const T &a){
  ostringstream oss;
  oss << a;
  return oss.str();
};
// ----------------------------------------------------------------------------

int main(){
  int N,K;
  cin >> N >> K;
  vector<vector<int>> G(N);
  for(int i=0; i<N-1; i++){
    int a,b;
    cin >> a >> b;
    a--;
    b--;
    G[a].push_back(b);
    G[b].push_back(a);
  }
  if(K > N){
    cout << -1 << endl;
    return 0;
  }
  queue<int> que;
  que.push(0);
  vector<int> dist(N,-1);
  dist[0] = 0;
  ll ans = 0;
  while(que.size()){
    int v = que.front();
    que.pop();
    for(int nv: G[v]){
      if(dist[nv] != -1) continue;
      dist[nv] = dist[v] + 1;
      if(K > 1){
        K--;
        ans++;
      }else{
        break;
      }
      que.push(nv);
    }
  }
  cout << ans << endl;
  return 0;
}