input: Write a python function to transfer money between two bank accounts.
  assert account1.balance == 1000
  assert account2.balance == 500
  account1.transfer_money(account2, 200)
  assert account1.balance == 800
  assert account2.balance == 700
  account2.transfer_money(account1, 100)
  assert account2.balance == 600
  assert account1.balance == 900
output: class BankAccount:
      def __init__(self, balance):
          self.balance = balance
  
      def transfer_money(self, other_account, amount):
          if self.balance >= amount:
              self.balance -= amount
              other_account.balance += amount
  
  # Example usage:
  account1 = BankAccount(1000)
  account2 = BankAccount(500)