#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <algorithm>
#include <set>
#include <map>
#include <bitset>
#include <cmath>
#include <functional>
#include <iomanip>
#define vll vector<ll>
#define vvvl vector<vvl>
#define vvl vector<vector<ll>>
#define VV(a, b, c, d) vector<vector<d>>(a, vector<d>(b, c))
#define VVV(a, b, c, d) vector<vvl>(a, vvl(b, vll (c, d)));
#define re(c, b) for(ll c=0;c<b;c++)
#define rep(a,b,c) for(ll a=b;a<c;a++)
#define all(obj) (obj).begin(), (obj).end()
typedef long long int ll;
typedef long double ld;
using namespace std;

void get(vll &a){re(i,a.size()) scanf("%lld",&a[i]);}
void get(vvl &a){re(i,a.size()) re(j,a[0].size()) scanf("%lld",&a[i][j]);}
void print(vll &a){re(i,a.size()) cout<<a[i]<<(i==a.size()-1?"\n":" ");}
void print(vvl &a){re(i,a.size()) re(j,a[0].size())cout<<a[i][j]<<(j==a[0].size()-1?"\n":" ");}


vvl G = VV(100001, 0, 0, ll);
ll cnt = 1;
ll ans = 0;
ll k;

void bfs(ll now, ll from, ll dist){
  for(auto to:G[now]){
    if(to==from) continue;
    if(cnt<k){
      cnt++;
      ans += dist+1;
    }
  }
  for(auto to:G[now]){
    if(to==from) continue;
    if(cnt<k){
      bfs(to, now, dist+1);
    }
  }
}
int main(int argc, char const *argv[]) {
  ll n;std::cin >> n >> k;
  re(i, n-1){
    ll a, b;std::cin >> a >> b;
    G[a].push_back(b);
    G[b].push_back(a);
  }
  if(n<k){
    std::cout << -1 << '\n';
    return 0;
  }
  std::cout << k-1 << '\n';
  return 0;
}