N,K = [int(i) for i in input().split()]
if N < K:
    print(-1)
    exit()
graph = {i:set() for i in range(1,N+1)}
for _ in range(N-1):
    a,b = [int(i) for i in input().split()]
    graph[a].add(b)
    graph[b].add(a)

que = [1]
seen = {1}
move = 0
while que:
    node = que.pop()
    for n in graph[node]:
        if n not in seen:
            seen.add(n)
            que.append(n)
            K -= 1
            if K != 0:
                move += 1
                break
    seen.add(node)
    if K == 0:
        break
print(move)