public static void main ( String [ ] args ) {
  Scanner s = new Scanner ( System . in ) ;
  String str = s . next ( ) ;
  int n = str . length ( ) , ca = 0 , co = 0 ;
  char [ ] a = str . toCharArray ( ) ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) if ( a [ i ] == 'a' ) ca ++ ;
  else co ++ ;
  while ( co >= ca ) co -- ;
  System . out . println ( co + ca ) ;
}

public static void main ( String [ ] args ) { Scanner s = new Scanner ( System . in ) ; String str = s . next ( ) ; int n = str . length ( ) , ca = 0 , co = 0 ; char [ ] a = str . toCharArray ( ) ; for ( int i = 0 ; i < n ; i ++ ) if ( a [ i ] == ' a ' ) ca ++ ; else co ++ ; while ( co >= ca ) co -- ; System . out . println ( co + ca ) ; }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (array_type element: (type_identifier) dimensions: (dimensions)) name: (identifier))) body: (block (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (type_identifier) arguments: (argument_list (field_access object: (identifier) field: (identifier)))))) (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list))) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal)) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (local_variable_declaration type: (array_type element: (integral_type) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) condition: (binary_expression left: (identifier) right: (identifier)) update: (update_expression (identifier)) body: (if_statement condition: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (character_literal))) consequence: (expression_statement (update_expression (identifier))) alternative: (expression_statement (update_expression (identifier))))) (while_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))) body: (expression_statement (update_expression (identifier)))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (identifier)))))))