from collections import deque

def setPro(t,c,cnt,r,v):
    v[node_t] = True
    if r[node_t] == 0:
        r[node_t] += 1
        c -= 1
    return (node_t,c,cnt+1,r,v)

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)
    elif coin < 0:
        continue
    for node_t in g[node_f]:
        if not visited[node_t]:
            que.append(setPro(node_t,coin,count,rec,visited))

if ans == 10**18:
    ans = -1

print(ans)