class NTree(object):
    def __init__(self):
        self.count = 0

    def constructor(self,N, K, edges, num):
        self.N = int(N)
        self.K = int(K)
        self.edges = edges
        self.num = num 
        if self.N < self.K:
            print(-1)
            exit()

    def run(self):
        sorted_num = dict(sorted(self.num.items(), key=lambda x:x[0]))
        K = self.K
        for key, value in sorted_num.items():
            if value >= K:
                self.count += K
                break
            else:
                self.count += value
                K = K - value
        print(self.count-1)

if __name__=="__main__":
    N, K = input().split(" ")
    edges= list()
    num  = dict()
    for i in range(1, int(N)):
        edge = list(map(int, input().split(" ")))
        edges.append(edge)
        if not edge[0] in num.keys():
            num[edge[0]]  = 1
        else:
            num[edge[0]] += 1
    func = NTree()
    func.constructor(N=N, K=K, edges=edges, num=num)
    func.run()