Buggy python submission (verdict: Runtime Error):
class UnionFind:
	def __init__(self, n):
		self.groups = [g for g in range(n)]

	def get_root(self, i):
		parent = self.groups[i]
		if parent == i:
			return parent
		else:
			root = self.get_root(parent)
			self.groups[i] = root
			return root
	
	def set_root(self, i, root):
		parent = self.groups[i]
		self.groups[i] = root
		if parent == i:
			return
		else:
			self.set_root(parent, root)
	
	def combine(self, i1, i2):
		self.set_root(i2, self.get_root(i1))
	
	def in_same_group(self, i1, i2):
		return self.get_root(i1) == self.get_root(i2)
	
	def to_dic(self):
		table = {}
		for i in range(len(self.groups)):
			g = self.get_root(i)
			if g in table:
				table[g].append(i)
			else:
				table[g] = [i]
		return table
	
	def to_list(self):
		table = self.to_dic()
		return [table[g] for g in table]





N, M = map(int, input().split())
ab_list = []
for i in range(N):
	a, b = map(int, input().split())
	ab_list.append((b, a))
ab_list.sort()
ab_list.reverse()

index_list = UnionFind(N)
used_list = [False] * M

reward = 0
for b, a in ab_list:
	index = M - a
	prev_index = None
	while index >= 0:
#		print(index, M, a, N)
		if not used_list[index]:
			used_list[index] = True
			reward += b
			break
		if prev_index != None:
			index_list.combine(index, prev_index)
		prev_index = index
		index = index_list.get_root(index) - 1

print(reward)


Fixed submission:
class UnionFind:
	def __init__(self, n):
		self.groups = [g for g in range(n)]

	def get_root(self, i):
		parent = self.groups[i]
		if parent == i:
			return parent
		else:
			root = self.get_root(parent)
			self.groups[i] = root
			return root
	
	def set_root(self, i, root):
		parent = self.groups[i]
		self.groups[i] = root
		if parent == i:
			return
		else:
			self.set_root(parent, root)
	
	def combine(self, i1, i2):
		self.set_root(i2, self.get_root(i1))
	
	def in_same_group(self, i1, i2):
		return self.get_root(i1) == self.get_root(i2)
	
	def to_dic(self):
		table = {}
		for i in range(len(self.groups)):
			g = self.get_root(i)
			if g in table:
				table[g].append(i)
			else:
				table[g] = [i]
		return table
	
	def to_list(self):
		table = self.to_dic()
		return [table[g] for g in table]





N, M = map(int, input().split())
ab_list = []
for i in range(N):
	a, b = map(int, input().split())
	ab_list.append((b, a))
ab_list.sort()
ab_list.reverse()

index_list = UnionFind(M)
used_list = [False] * M

reward = 0
for b, a in ab_list:
	index = M - a
	prev_index = None
	while index >= 0:
#		print(index, M, a, N)
		if not used_list[index]:
			used_list[index] = True
			reward += b
			break
		if prev_index != None:
			index_list.combine(index, prev_index)
		prev_index = index
		index = index_list.get_root(index) - 1

print(reward)

Buggy python submission (verdict: Runtime Error):
class UnionFind:
	def __init__(self, n):
		self.groups = [g for g in range(n)]

	def get_root(self, i):
		parent = self.groups[i]
		if parent == i:
			return parent
		else:
			root = self.get_root(parent)
			self.groups[i] = root
			return root
	
	def set_root(self, i, root):
		parent = self.groups[i]
		self.groups[i] = root
		if parent == i:
			return
		else:
			self.set_root(parent, root)
	
	def combine(self, i1, i2):
		self.set_root(i2, self.get_root(i1))
	
	def in_same_group(self, i1, i2):
		return self.get_root(i1) == self.get_root(i2)
	
	def to_dic(self):
		table = {}
		for i in range(len(self.groups)):
			g = self.get_root(i)
			if g in table:
				table[g].append(i)
			else:
				table[g] = [i]
		return table
	
	def to_list(self):
		table = self.to_dic()
		return [table[g] for g in table]





N, M = map(int, input().split())
ab_list = []
for i in range(N):
	a, b = map(int, input().split())
	ab_list.append((b, a))
ab_list.sort()
ab_list.reverse()

index_list = UnionFind(N)
used_list = [False] * N

reward = 0
for b, a in ab_list:
	index = M - a
#	print("i", index, a)
	prev_index = None
	while index >= 0:
		if not used_list[index]:
			break
		if prev_index != None:
			index_list.combine(index, prev_index)
		prev_index = index
		index = index_list.get_root(index) - 1
		
#	print(index)
	if index >= 0:
		used_list[index] = True
		reward += b

print(reward)


Fixed submission:
class UnionFind:
	def __init__(self, n):
		self.groups = [g for g in range(n)]

	def get_root(self, i):
		parent = self.groups[i]
		if parent == i:
			return parent
		else:
			root = self.get_root(parent)
			self.groups[i] = root
			return root
	
	def set_root(self, i, root):
		parent = self.groups[i]
		self.groups[i] = root
		if parent == i:
			return
		else:
			self.set_root(parent, root)
	
	def combine(self, i1, i2):
		self.set_root(i2, self.get_root(i1))
	
	def in_same_group(self, i1, i2):
		return self.get_root(i1) == self.get_root(i2)
	
	def to_dic(self):
		table = {}
		for i in range(len(self.groups)):
			g = self.get_root(i)
			if g in table:
				table[g].append(i)
			else:
				table[g] = [i]
		return table
	
	def to_list(self):
		table = self.to_dic()
		return [table[g] for g in table]





N, M = map(int, input().split())
ab_list = []
for i in range(N):
	a, b = map(int, input().split())
	ab_list.append((b, a))
ab_list.sort()
ab_list.reverse()

index_list = UnionFind(M)
used_list = [False] * M

reward = 0
for b, a in ab_list:
	index = M - a
	prev_index = None
	while index >= 0:
#		print(index, M, a, N)
		if not used_list[index]:
			used_list[index] = True
			reward += b
			break
		if prev_index != None:
			index_list.combine(index, prev_index)
		prev_index = index
		index = index_list.get_root(index) - 1

print(reward)

Buggy python submission (verdict: Runtime Error):
class UnionFind:
	def __init__(self, n):
		self.groups = [g for g in range(n)]

	def get_root(self, i):
		parent = self.groups[i]
		if parent == i:
			return parent
		else:
			root = self.get_root(parent)
			self.groups[i] = root
			return root
	
	def set_root(self, i, root):
		parent = self.groups[i]
		self.groups[i] = root
		if parent == i:
			return
		else:
			self.set_root(parent, root)
	
	def combine(self, i1, i2):
		self.set_root(i2, self.get_root(i1))
	
	def in_same_group(self, i1, i2):
		return self.get_root(i1) == self.get_root(i2)
	
	def to_dic(self):
		table = {}
		for i in range(len(self.groups)):
			g = self.get_root(i)
			if g in table:
				table[g].append(i)
			else:
				table[g] = [i]
		return table
	
	def to_list(self):
		table = self.to_dic()
		return [table[g] for g in table]





N, M = map(int, input().split())
ab_list = []
for i in range(N):
	a, b = map(int, input().split())
	ab_list.append((b, a))
ab_list.sort()
ab_list.reverse()

index_list = UnionFind(N)
used_list = [False] * N

reward = 0
for b, a in ab_list:
	index = M - a
#	print("i", index, a)
	prev_index = None
	while True:
		if not used_list[index]:
			break
		if prev_index != None:
			index_list.combine(index, prev_index)
		prev_index = index
		index = index_list.get_root(index) - 1
		
#	print(index)
	if index >= 0:
		used_list[index] = True
		reward += b

print(reward)


Fixed submission:
class UnionFind:
	def __init__(self, n):
		self.groups = [g for g in range(n)]

	def get_root(self, i):
		parent = self.groups[i]
		if parent == i:
			return parent
		else:
			root = self.get_root(parent)
			self.groups[i] = root
			return root
	
	def set_root(self, i, root):
		parent = self.groups[i]
		self.groups[i] = root
		if parent == i:
			return
		else:
			self.set_root(parent, root)
	
	def combine(self, i1, i2):
		self.set_root(i2, self.get_root(i1))
	
	def in_same_group(self, i1, i2):
		return self.get_root(i1) == self.get_root(i2)
	
	def to_dic(self):
		table = {}
		for i in range(len(self.groups)):
			g = self.get_root(i)
			if g in table:
				table[g].append(i)
			else:
				table[g] = [i]
		return table
	
	def to_list(self):
		table = self.to_dic()
		return [table[g] for g in table]





N, M = map(int, input().split())
ab_list = []
for i in range(N):
	a, b = map(int, input().split())
	ab_list.append((b, a))
ab_list.sort()
ab_list.reverse()

index_list = UnionFind(M)
used_list = [False] * M

reward = 0
for b, a in ab_list:
	index = M - a
	prev_index = None
	while index >= 0:
#		print(index, M, a, N)
		if not used_list[index]:
			used_list[index] = True
			reward += b
			break
		if prev_index != None:
			index_list.combine(index, prev_index)
		prev_index = index
		index = index_list.get_root(index) - 1

print(reward)