import sys
input = sys.stdin.readline

n, k = map(int, input().split())
g = [[] for _ in range(n)]
for i in range(n-1):
    a, b = map(int, input().split())
    a, b = a-1, b-1
    g[a].append(b)
    g[b].append(a)
#print(g)

if k > n:
    print(-1)
    exit()

from collections import deque
q = deque()
q.append(0)
visit = [0]*n
cnt = 0
visit[0] = 1
while q:
    x = q.popleft()
    for new_x in g[x]:
        if visit[new_x] == 0:
            cnt += 1
            visit[new_x] = 1
            q.append(new_x)
        if cnt == k-1:
            print(sum(visit)-1)
            #print(visit)
            exit()
#print(cnt)
#print(visit)