public static void main ( String [ ] args ) {
  Scanner scanner = new Scanner ( System . in ) ;
  String s = scanner . next ( ) ;
  String newstr = s . replaceAll ( "a" , "" ) ;
  int removedcharlength = s . length ( ) - newstr . length ( ) ;
  int midindex = newstr . length ( ) / 2 ;
  if ( newstr . substring ( 0 , midindex ) . equals ( newstr . substring ( midindex ) ) ) {
    String strz = s . substring ( 0 , midindex + removedcharlength ) . replaceAll ( "a" , "" ) ;
    if ( s . substring ( midindex + removedcharlength ) . equals ( strz ) ) System . out . println ( s . substring ( 0 , midindex + removedcharlength ) ) ;
    else System . out . println ( ":(" ) ;
  }
  else System . out . println ( ":(" ) ;
}

public static void main ( String [ ] args ) { Scanner scanner = new Scanner ( System . in ) ; String s = scanner . next ( ) ; String newstr = s . replaceAll ( " a " , " " ) ; int removedcharlength = s . length ( ) - newstr . length ( ) ; int midindex = newstr . length ( ) / 2 ; if ( newstr . substring ( 0 , midindex ) . equals ( newstr . substring ( midindex ) ) ) { String strz = s . substring ( 0 , midindex + removedcharlength ) . replaceAll ( " a " , " " ) ; if ( s . substring ( midindex + removedcharlength ) . equals ( strz ) ) System . out . println ( s . substring ( 0 , midindex + removedcharlength ) ) ; else System . out . println ( " : ( " ) ; } else System . out . println ( " : ( " ) ; }
(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: (type_identifier) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (string_literal) (string_literal))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) right: (decimal_integer_literal)))) (if_statement condition: (parenthesized_expression (method_invocation object: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (decimal_integer_literal) (identifier))) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier)))))) consequence: (block (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (decimal_integer_literal) (binary_expression left: (identifier) right: (identifier)))) name: (identifier) arguments: (argument_list (string_literal) (string_literal))))) (if_statement condition: (parenthesized_expression (method_invocation object: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (identifier)))) name: (identifier) arguments: (argument_list (identifier)))) consequence: (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (decimal_integer_literal) (binary_expression left: (identifier) right: (identifier))))))) alternative: (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal)))))) alternative: (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal)))))))