Buggy python submission (verdict: Time Limit Exceeded):
from sys import setrecursionlimit
setrecursionlimit(100000)
def rad_reach(b,h,dist,E,rad):
	cnt = 1
	if dist < rad:
		for nxt in E[h]:
			if nxt == b:
				continue
			cnt += rad_reach(h,nxt,dist+1,E,rad) 
	return cnt
def solve():
	N,K = map(int,raw_input().split())
	pairs = []
	E = [[] for i in xrange(N)]
	for i in xrange(N-1):
		a,b = map(lambda x:int(x)-1,raw_input().split())
		E[a].append(b)
		E[b].append(a)
		pairs.append((a,b))
	ans = N
	rad = K/2
	if K % 2 == 0:
		for c in xrange(N):
			ans = min(ans,N-rad_reach(-1,c,0,E,rad))
	else:
		for c1,c2 in pairs:
			ans = min(ans,N-rad_reach(c2,c1,0,E,rad)-rad_reach(c1,c2,0,E,rad))
	print ans
solve()

Fixed submission:
from sys import setrecursionlimit
setrecursionlimit(1000000)
def calc_dist(b,h,dist,E,D,ne):
	D[dist] += 1
	for nxt in E[h]:
		if nxt == b or nxt == ne:
			continue
		calc_dist(h,nxt,dist+1,E,D,ne) 

def solve():
	N,K = map(int,raw_input().split())
	pairs = []
	E = [[] for i in xrange(N)]
	for i in xrange(N-1):
		a,b = map(lambda x:int(x)-1,raw_input().split())
		E[a].append(b)
		E[b].append(a)
		pairs.append((a,b))
	ans = N
	rad = K/2
	if K % 2 == 0:
		for i in xrange(N):
			D = [0]*N
			calc_dist(-1,i,0,E,D,-1)
			for j in xrange(rad):
				D[rad-j-1] += D[rad-j]
			ans = min(N-D[0],ans)
	else:
		for a,b in pairs:
			D1 = [0]*N
			D2 = [0]*N
			calc_dist(-1,a,0,E,D1,b)
			calc_dist(-1,b,0,E,D2,a)
			for j in xrange(rad):
				D1[rad-j-1] += D1[rad-j]
				D2[rad-j-1] += D2[rad-j]
			ans = min(N-D1[0]-D2[0],ans)
	print ans

solve()

Buggy python submission (verdict: Time Limit Exceeded):
from sys import setrecursionlimit
setrecursionlimit(100000)
def rad_reach(b,h,dist,E,rad):
	cnt = 1
	if dist < rad:
		for nxt in E[h]:
			if nxt == b:
				continue
			cnt += rad_reach(h,nxt,dist+1,E,rad) 
	return cnt
def solve():
	N,K = map(int,raw_input().split())
	pairs = []
	E = [[] for i in xrange(N)]
	for i in xrange(N-1):
		a,b = map(lambda x:int(x)-1,raw_input().split())
		E[a].append(b)
		E[b].append(a)
		pairs.append((a,b))
	ans = N
	rad = K/2
	if K % 2 == 0:
		for c in xrange(N):
			ans = min(ans,N-rad_reach(-1,c,0,E,rad))
	else:
		for c1,c2 in pairs:
			ans = min(ans,N-rad_reach(c2,c1,0,E,rad)-rad_reach(c1,c2,0,E,rad))
	print ans
solve()

Fixed submission:
from sys import setrecursionlimit
setrecursionlimit(1000000)
def calc_dist(b,h,dist,E,D,ne):
	D[dist] += 1
	for nxt in E[h]:
		if nxt == b or nxt == ne:
			continue
		calc_dist(h,nxt,dist+1,E,D,ne) 

def solve():
	N,K = map(int,raw_input().split())
	pairs = []
	E = [[] for i in xrange(N)]
	for i in xrange(N-1):
		a,b = map(lambda x:int(x)-1,raw_input().split())
		E[a].append(b)
		E[b].append(a)
		pairs.append((a,b))
	ans = N
	rad = K/2
	if K % 2 == 0:
		for i in xrange(N):
			D = [0]*N
			calc_dist(-1,i,0,E,D,-1)
			for j in xrange(rad):
				D[rad-j-1] += D[rad-j]
			ans = min(N-D[0],ans)
	else:
		for a,b in pairs:
			D1 = [0]*N
			D2 = [0]*N
			calc_dist(-1,a,0,E,D1,b)
			calc_dist(-1,b,0,E,D2,a)
			for j in xrange(rad):
				D1[rad-j-1] += D1[rad-j]
				D2[rad-j-1] += D2[rad-j]
			ans = min(N-D1[0]-D2[0],ans)
	print ans

solve()

Buggy python submission (verdict: Time Limit Exceeded):
from sys import setrecursionlimit
setrecursionlimit(100000)
def rad_reach(bfr,h,dist,E,rad,ne):
	cnt = 1
	if dist < rad:
		for nxt in E[h]:
			if nxt == bfr: continue
			cnt += rad_reach(h,nxt,dist+1,E,rad,ne) 
	return cnt
def solve():
	N,K = map(int,raw_input().split())
	pairs = []
	E = [set() for i in xrange(N)]
	for i in xrange(N-1):
		a,b = map(lambda x:int(x)-1,raw_input().split())
		E[a].add(b)
		E[b].add(a)
		pairs.append((a,b))
	ans = N
	rad = K/2
	if K % 2 == 0:
		for c in xrange(N):
			ans = min(ans,N-rad_reach(-1,c,0,E,rad,-1))
	else:
		for c1,c2 in pairs:
			E[c1].remove(c2); E[c2].remove(c1)
			ans = min(ans,N-rad_reach(-1,c1,0,E,rad,c2)-rad_reach(-1,c2,0,E,rad,c1))
			E[c1].add(c2); E[c2].add(c1)
	print ans
solve()

Fixed submission:
from sys import setrecursionlimit
setrecursionlimit(1000000)
def calc_dist(b,h,dist,E,D,ne):
	D[dist] += 1
	for nxt in E[h]:
		if nxt == b or nxt == ne:
			continue
		calc_dist(h,nxt,dist+1,E,D,ne) 

def solve():
	N,K = map(int,raw_input().split())
	pairs = []
	E = [[] for i in xrange(N)]
	for i in xrange(N-1):
		a,b = map(lambda x:int(x)-1,raw_input().split())
		E[a].append(b)
		E[b].append(a)
		pairs.append((a,b))
	ans = N
	rad = K/2
	if K % 2 == 0:
		for i in xrange(N):
			D = [0]*N
			calc_dist(-1,i,0,E,D,-1)
			for j in xrange(rad):
				D[rad-j-1] += D[rad-j]
			ans = min(N-D[0],ans)
	else:
		for a,b in pairs:
			D1 = [0]*N
			D2 = [0]*N
			calc_dist(-1,a,0,E,D1,b)
			calc_dist(-1,b,0,E,D2,a)
			for j in xrange(rad):
				D1[rad-j-1] += D1[rad-j]
				D2[rad-j-1] += D2[rad-j]
			ans = min(N-D1[0]-D2[0],ans)
	print ans

solve()

Buggy python submission (verdict: Time Limit Exceeded):
from sys import setrecursionlimit
setrecursionlimit(100000)
def rad_reach(b,h,dist,E,rad,ne):
	cnt = 1
	if dist < rad:
		for nxt in E[h]:
			if nxt == b or nxt == ne:
				continue
			cnt += rad_reach(h,nxt,dist+1,E,rad,ne) 
	return cnt
def solve():
	N,K = map(int,raw_input().split())
	pairs = []
	E = [[] for i in xrange(N)]
	for i in xrange(N-1):
		a,b = map(lambda x:int(x)-1,raw_input().split())
		E[a].append(b)
		E[b].append(a)
		pairs.append((a,b))
	ans = N
	rad = K/2
	if K % 2 == 0:
		for c in xrange(N):
			ans = min(ans,N-rad_reach(-1,c,0,E,rad,-1))
	else:
		for c1,c2 in pairs:
			ans = min(ans,N-rad_reach(-1,c1,0,E,rad,c2)-rad_reach(-1,c2,0,E,rad,c1))
	print ans
solve()

Fixed submission:
from sys import setrecursionlimit
setrecursionlimit(1000000)
def calc_dist(b,h,dist,E,D,ne):
	D[dist] += 1
	for nxt in E[h]:
		if nxt == b or nxt == ne:
			continue
		calc_dist(h,nxt,dist+1,E,D,ne) 

def solve():
	N,K = map(int,raw_input().split())
	pairs = []
	E = [[] for i in xrange(N)]
	for i in xrange(N-1):
		a,b = map(lambda x:int(x)-1,raw_input().split())
		E[a].append(b)
		E[b].append(a)
		pairs.append((a,b))
	ans = N
	rad = K/2
	if K % 2 == 0:
		for i in xrange(N):
			D = [0]*N
			calc_dist(-1,i,0,E,D,-1)
			for j in xrange(rad):
				D[rad-j-1] += D[rad-j]
			ans = min(N-D[0],ans)
	else:
		for a,b in pairs:
			D1 = [0]*N
			D2 = [0]*N
			calc_dist(-1,a,0,E,D1,b)
			calc_dist(-1,b,0,E,D2,a)
			for j in xrange(rad):
				D1[rad-j-1] += D1[rad-j]
				D2[rad-j-1] += D2[rad-j]
			ans = min(N-D1[0]-D2[0],ans)
	print ans

solve()

Buggy python submission (verdict: Runtime Error):
def calc_dist(b,h,dist,E,D,ne):
	D[dist] += 1
	for nxt in E[h]:
		if nxt == b or nxt == ne:
			continue
		calc_dist(h,nxt,dist+1,E,D,ne) 

def solve():
	N,K = map(int,raw_input().split())
	pairs = []
	E = [[] for i in xrange(N)]
	for i in xrange(N-1):
		a,b = map(lambda x:int(x)-1,raw_input().split())
		E[a].append(b)
		E[b].append(a)
		pairs.append((a,b))
	ans = N
	rad = K/2
	if K % 2 == 0:
		for i in xrange(N):
			D = [0]*N
			calc_dist(-1,i,0,E,D,-1)
			for j in xrange(rad):
				D[rad-j-1] += D[rad-j]
			ans = min(N-D[0],ans)
	else:
		for a,b in pairs:
			D1 = [0]*N
			D2 = [0]*N
			calc_dist(-1,a,0,E,D1,b)
			calc_dist(-1,b,0,E,D2,a)
			for j in xrange(rad):
				D1[rad-j-1] += D1[rad-j]
				D2[rad-j-1] += D2[rad-j]
			ans = min(N-D1[0]-D2[0],ans)
	print ans

solve()

Fixed submission:
from sys import setrecursionlimit
setrecursionlimit(1000000)
def calc_dist(b,h,dist,E,D,ne):
	D[dist] += 1
	for nxt in E[h]:
		if nxt == b or nxt == ne:
			continue
		calc_dist(h,nxt,dist+1,E,D,ne) 

def solve():
	N,K = map(int,raw_input().split())
	pairs = []
	E = [[] for i in xrange(N)]
	for i in xrange(N-1):
		a,b = map(lambda x:int(x)-1,raw_input().split())
		E[a].append(b)
		E[b].append(a)
		pairs.append((a,b))
	ans = N
	rad = K/2
	if K % 2 == 0:
		for i in xrange(N):
			D = [0]*N
			calc_dist(-1,i,0,E,D,-1)
			for j in xrange(rad):
				D[rad-j-1] += D[rad-j]
			ans = min(N-D[0],ans)
	else:
		for a,b in pairs:
			D1 = [0]*N
			D2 = [0]*N
			calc_dist(-1,a,0,E,D1,b)
			calc_dist(-1,b,0,E,D2,a)
			for j in xrange(rad):
				D1[rad-j-1] += D1[rad-j]
				D2[rad-j-1] += D2[rad-j]
			ans = min(N-D1[0]-D2[0],ans)
	print ans

solve()

Buggy python submission (verdict: Time Limit Exceeded):
def calc_dist(b,h,dist,E,D,ne):
	D[dist] += 1
	for nxt in E[h]:
		if nxt == b or nxt == ne:
			continue
		calc_dist(h,nxt,dist+1,E,D,ne) 

def solve():
	N,K = map(int,raw_input().split())
	pairs = []
	E = [[] for i in xrange(N)]
	for i in xrange(N-1):
		a,b = map(lambda x:int(x)-1,raw_input().split())
		E[a].append(b)
		E[b].append(a)
		pairs.append((a,b))
	ans = N
	rad = K/2
	if K % 2 == 0:
		for i in xrange(N):
			D = [0]*N
			calc_dist(-1,i,0,E,D,-1)
			for j in xrange(rad):
				D[rad-j-1] += D[rad-j]
			ans = min(N-D[0],ans)
	else:
		for a,b in pairs:
			D1 = [0]*N
			D2 = [0]*N
			calc_dist(-1,a,0,E,D1,b)
			calc_dist(-1,b,0,E,D2,a)
			for j in xrange(rad):
				D1[rad-j-1] += D1[rad-j]
				D2[rad-j-1] += D2[rad-j]
			ans = min(N-D1[0]-D2[0],ans)
	print ans

solve()

Fixed submission:
from sys import setrecursionlimit
setrecursionlimit(1000000)
def calc_dist(b,h,dist,E,D,ne):
	D[dist] += 1
	for nxt in E[h]:
		if nxt == b or nxt == ne:
			continue
		calc_dist(h,nxt,dist+1,E,D,ne) 

def solve():
	N,K = map(int,raw_input().split())
	pairs = []
	E = [[] for i in xrange(N)]
	for i in xrange(N-1):
		a,b = map(lambda x:int(x)-1,raw_input().split())
		E[a].append(b)
		E[b].append(a)
		pairs.append((a,b))
	ans = N
	rad = K/2
	if K % 2 == 0:
		for i in xrange(N):
			D = [0]*N
			calc_dist(-1,i,0,E,D,-1)
			for j in xrange(rad):
				D[rad-j-1] += D[rad-j]
			ans = min(N-D[0],ans)
	else:
		for a,b in pairs:
			D1 = [0]*N
			D2 = [0]*N
			calc_dist(-1,a,0,E,D1,b)
			calc_dist(-1,b,0,E,D2,a)
			for j in xrange(rad):
				D1[rad-j-1] += D1[rad-j]
				D2[rad-j-1] += D2[rad-j]
			ans = min(N-D1[0]-D2[0],ans)
	print ans

solve()