from collections import deque

n,k = map(int,input().split())

ab = [[] for i in range(n)]
for i in range(n-1):
    a,b = map(int,input().split())
    a -= 1
    b -= 1
    ab[a].append(b)
    ab[b].append(a)

d = deque()
d.append([0,0])
chk = [0]*(n)
chk[0] = 1

f = False
cnt = 0

while f == False and len(d) > 0:
    tmp,num = d.popleft()
    for i in ab[tmp]:
        if chk[i] == 0:
            chk[i] = 1
            d.append([i,num+1])
            k -= 1
            cnt += 1
            if k == 1:
                f = True
                break
#print(k)
if f == True:
    print(cnt)
else:
    print(-1)