import collections

def main():
    n, k = map(int, input().split())
    e = [list(map(int, input().split())) for _ in range(n - 1)]
    ans = solve(n, k, e)
    print(ans)


def solve(n, k, e):
    if n < k:
        return -1
    g = [[] for _ in range(n)]
    for (x, y) in e:
        x, y = x - 1, y - 1
        g[x].append(y)
        g[y].append(x)

    arrived = [False for _ in range(n)]
    q = collections.deque()
    q.append(0)
    coins = 0
    ans = -1
    while len(q):
        v = q.popleft()
        if not arrived[v]:
            arrived[v] = True
            coins += 1
            ans += 1
            if coins == k:
                break
            for i in g[v]:
                q.append(i)
    else:
        return -1
    return ans

if __name__ == '__main__':
    main()