import java.util.*;

class Main{
    static int INF=100000007;
    static class edge implements Comparable<edge>{
        int from;
        int to;
        
        void edge(int from,int to){
            this.from=from;
            this.to=to;
        }
        
        public int compareTo(edge e){
            return this.from-e.from;
        }
    }
    
    public static void main(String[] args){
        Scanner sc=new Scanner(System.in);
        int N=sc.nextInt();
        int K=sc.nextInt();
        edge[] graph=new edge[N-1];
        int[] dist=new int[N];
        
        for(int i=0;i<N;i++){
            dist[i]=INF;
        }
        
        dist[0]=0;
        
        for(int i=0;i<N-1;i++){
            edge e=new edge();
            e.edge(sc.nextInt()-1,sc.nextInt()-1);
            graph[i]=e;
        }
        
        Arrays.sort(graph);
        
        boolean change=false;
        
        while(true){
            change=false;
            for(int i=0;i<N-1;i++){
                int start=graph[i].from;
                int end=graph[i].to;
                
                if(dist[start]!=INF&&dist[end]>dist[start]+1){
                    dist[end]=dist[start]+1;
                    change=true;
                }
            }
            
            if(!change){
                break;
            }
        }
        
        int count=0;
        
        for(int i=0;i<N;i++){
            if(dist[i]!=INF){
                count++;
            }
        }
        
        if(count<K){
            System.out.println("-1");
            return;
        }
        
        Arrays.sort(dist);
        int ans=0;
        int current=0;
        boolean check=false;
        
        for(int i=0;i<K;i++){
            current=dist[i];
            if(dist[i]==current&&check){
                ans++;
            }
            if(dist[i]==current&&!check){
                check=true;
            }
            if(dist[i]!=current){
                current=dist[i];
                check=false;
            }
        }
        
        System.out.println(ans);
    }
}