from collections import deque

N,K = map(int,input().split())
g = [[] for _ in range(N)]

for _ in range(N-1):
    a,b = map(int,input().split())
    a -= 1
    b -= 1
    g[a].append(b)
    g[b].append(a)

summary = [0]*N
summary[0] = 1
que = deque([(0,K-1,0,summary,[False]*N)])
ans = 10**18

while que:
    node_f,coin,count,rec,visited = que.popleft()
    if coin == 0:
        ans = min(ans,count)
    for node_t in g[node_f]:
        if not visited[node_t]:
            c = coin
            visited[node_t] = True
            if rec[node_t] == 0:
                rec[node_t] += 1
                c -= 1
            que.append((node_t,c,count+1,rec,visited))

if ans == 10**18:
    ans = -1
    
print(ans)