Buggy python submission (verdict: Time Limit Exceeded):
A,B=map(int,input().split())

def int_to_bit(N):
  lst=[]
  ans=''
  if N==0:
    return 0
  while N!=1 and N!=0:
    lst.append(str(N%2))
    N//=2
  for i in range(1,len(lst)+1):
    ans+=lst[-i]
  if N==0:
    pass
  else:
    ans='1'+ans
  return int(ans)

def bit_to_int(N):
  N=str(N)
  ans=0
  for i in range(len(N)):
    ans+=int(N[i])*2**(len(N)-1-i)
  return ans

def XOR(a,b):
  a,b=min(a,b),max(a,b)
  a,b=str(a),str(b)
  length=len(a)
  lst=[]
  ans=''
  for i in range(1,length+1):
    if a[-i]==b[-i]=='1' or a[-i]==b[-i]=='0':
      lst.append('0')
    else:
      lst.append('1')
  for i in range(1,length+1):        # ここ下手
    ans+=lst[-i]
  if length==len(b):
    pass
  else:
    add=b[0:len(b)-length]
    ans=add+ans
  return ans

List=[A+i for i in range(B-A+1)]
while len(List)>1:
  v1=int_to_bit(List[0])
  v2=int_to_bit(List[1])
  v=bit_to_int(XOR(v1,v2))        # ここ下手
  List.pop(0)
  List.pop(0)
  List.insert(0,v)
  
print(List[0])

Fixed submission:
A,B=map(int,input().split())

def int_to_bit(N):
  lst=[]
  ans=''
  if N==0:
    return 0
  while N!=1 and N!=0:
    lst.append(str(N%2))
    N//=2
  for i in range(1,len(lst)+1):
    ans+=lst[-i]
  if N==0:
    pass
  else:
    ans='1'+ans
  return int(ans)

def bit_to_int(N):
  N=str(N)
  ans=0
  for i in range(len(N)):
    ans+=int(N[i])*2**(len(N)-1-i)
  return ans

def XOR(a,b):
  a,b=min(a,b),max(a,b)
  a,b=str(a),str(b)
  length=len(a)
  lst=[]
  ans=''
  for i in range(1,length+1):
    if a[-i]==b[-i]=='1' or a[-i]==b[-i]=='0':
      lst.append('0')
    else:
      lst.append('1')
  for i in range(1,length+1):        
    ans+=lst[-i]
  if length==len(b):
    pass
  else:
    add=b[0:len(b)-length]
    ans=add+ans
  return bit_to_int(ans)

if A%2==0 and B%2==0:
  v=(B-A)//2
  if v%2==0:
    print(B)
  else:
    print(XOR(1,int_to_bit(B)))
elif A%2==0 and B%2==1:
  v=(B-A+1)//2
  if v%2==0:
    print(0)
  else:
    print(1)
elif A%2==1 and B%2==0:
  v=(B-1-A)//2
  if v%2==0:
    print(XOR(int_to_bit(A),int_to_bit(B)))
  else:
    print(XOR(1,int_to_bit(XOR(int_to_bit(A),int_to_bit(B)))))
else:
  v=(B-A)//2
  if v%2==0:
    print(A)
  else:
    print(XOR(int_to_bit(A),1))

Buggy python submission (verdict: Runtime Error):
A,B=map(int,input().split())

def int_to_bit(N):
  lst=[]
  ans=''
  while N!=1 and N!=0:
    lst.append(str(N%2))
    N//=2
  for i in range(1,len(lst)+1):
    ans+=lst[-i]
  if N==0:
    pass
  else:
    ans='1'+ans
  return int(ans)

def bit_to_int(N):
  N=str(N)
  ans=0
  for i in range(len(N)):
    ans+=int(N[i])*2**(len(N)-1-i)
  return ans

def XOR(a,b):
  a,b=min(a,b),max(a,b)
  a,b=str(a),str(b)
  length=len(a)
  lst=[]
  ans=''
  for i in range(1,length+1):
    if a[-i]==b[-i]=='1' or a[-i]==b[-i]=='0':
      lst.append('0')
    else:
      lst.append('1')
  for i in range(1,length+1):        # ここ下手
    ans+=lst[-i]
  if length==len(b):
    pass
  else:
    add=b[0:len(b)-length]
    ans=add+ans
  return ans

List=[A+i for i in range(B-A+1)]
while len(List)>1:
  v1=int_to_bit(List[0])
  v2=int_to_bit(List[1])
  v=bit_to_int(XOR(v1,v2))        # ここ下手
  List.pop(0)
  List.pop(0)
  List.insert(0,v)
  
print(List[0])

Fixed submission:
A,B=map(int,input().split())

def int_to_bit(N):
  lst=[]
  ans=''
  if N==0:
    return 0
  while N!=1 and N!=0:
    lst.append(str(N%2))
    N//=2
  for i in range(1,len(lst)+1):
    ans+=lst[-i]
  if N==0:
    pass
  else:
    ans='1'+ans
  return int(ans)

def bit_to_int(N):
  N=str(N)
  ans=0
  for i in range(len(N)):
    ans+=int(N[i])*2**(len(N)-1-i)
  return ans

def XOR(a,b):
  a,b=min(a,b),max(a,b)
  a,b=str(a),str(b)
  length=len(a)
  lst=[]
  ans=''
  for i in range(1,length+1):
    if a[-i]==b[-i]=='1' or a[-i]==b[-i]=='0':
      lst.append('0')
    else:
      lst.append('1')
  for i in range(1,length+1):        
    ans+=lst[-i]
  if length==len(b):
    pass
  else:
    add=b[0:len(b)-length]
    ans=add+ans
  return bit_to_int(ans)

if A%2==0 and B%2==0:
  v=(B-A)//2
  if v%2==0:
    print(B)
  else:
    print(XOR(1,int_to_bit(B)))
elif A%2==0 and B%2==1:
  v=(B-A+1)//2
  if v%2==0:
    print(0)
  else:
    print(1)
elif A%2==1 and B%2==0:
  v=(B-1-A)//2
  if v%2==0:
    print(XOR(int_to_bit(A),int_to_bit(B)))
  else:
    print(XOR(1,int_to_bit(XOR(int_to_bit(A),int_to_bit(B)))))
else:
  v=(B-A)//2
  if v%2==0:
    print(A)
  else:
    print(XOR(int_to_bit(A),1))