def main():
    N, K = (int(i) for i in input().split())
    G = [[] for _ in range(N)]
    for _ in range(N-1):
        a, b = (int(i)-1 for i in input().split())
        G[a].append(b)
        G[b].append(a)
    from collections import deque

    def bfs(s, K):
        dist = [-1 for _ in range(len(G))]
        que = deque()
        dist[s] = 0
        K -= 1
        ans = 0
        que.append(s)
        while que and K > 0:
            u = que.popleft()
            for v in G[u]:
                if dist[v] != -1:
                    continue
                dist[v] = dist[u] + 1
                K -= 1
                ans += 1
                que.append(v)
                if K == 0:
                    break
        return ans
    if N < K:
        return print(-1)
    ans = bfs(0, K)
    print(ans)


if __name__ == '__main__':
    main()