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)
que = deque([(0,K,0,[0]*N)])
ans = 10**18
while que:
    node_f,coin,count,rec = que.pop()
    if coin == 1:
        ans = min(ans,count)
    for node_t in g[node_f]:
        if node_t == 0 or rec[node_t] == 0:
            rec[node_t] += 1
            que.append((node_t,coin-1,count+1,rec))
if ans == 10**18:
    ans = -1
print(ans)