import math
import sys
def S(): return sys.stdin.readline().rstrip()
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int, sys.stdin.readline().rstrip().split())
def LI(): return list(map(int, sys.stdin.readline().rstrip().split()))
def LS(): return list(sys.stdin.readline().rstrip().split())

n, k = MI()
x = {}
for i in range(n-1):
    a, b = MI()
    if a-1 in x:
        x[a-1].append(b-1)
    else:
        x[a-1] = [b-1]
    if b-1 in x:
        x[b-1].append(a-1)
    else:
        x[b-1] = [a-1]

from collections import deque
d = deque()
s = [0]*n

d.append(0)

while d:
    y = d.pop()
    for i in x[y]:
        if s[i] == 0:
            s[i] = 1
            d.append(i)


if sum(s) < k:
    print(-1)
else:
    print(k-1)