class Account
{
  public string owner;      // anyone can read or change this
  private double balance;   // only Account code can touch this

  public void Deposit(double amount)
  {
    balance = balance + amount;   // allowed: same class
  }

  public double GetBalance()
  {
    return balance;
  }
}

class Program
{
  static void Main()
  {
    Account a = new Account();
    a.owner = "Sam";          // OK: public
    a.Deposit(100);           // OK: public method
    // a.balance = 999;       // ERROR: balance is private
    Console.WriteLine(a.GetBalance());  // 100
  }
}