public static void main ( String [ ] args ) {
  Scanner in = new Scanner ( System . in ) ;
  String t = in . next ( ) ;
  String s = t . substring ( 0 , ( int ) ( t . length ( ) + t . chars ( ) . filter ( c -> c == 'a' ) . count ( ) ) / 2 ) ;
  System . out . println ( t . equals ( s + s . replaceAll ( "a" , "" ) ) ? s : ":(" ) ;
}

public static void main ( String [ ] args ) { Scanner in = new Scanner ( System . in ) ; String t = in . next ( ) ; String s = t . substring ( 0 , ( int ) ( t . length ( ) + t . chars ( ) . filter ( c -> c == ' a ' ) . count ( ) ) / 2 ) ; System . out . println ( t . equals ( s + s . replaceAll ( " a " , " " ) ) ? s : " : ( " ) ; }
(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 (decimal_integer_literal) (binary_expression left: (cast_expression type: (integral_type) value: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) right: (method_invocation object: (method_invocation object: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) name: (identifier) arguments: (argument_list (lambda_expression parameters: (identifier) body: (binary_expression left: (identifier) right: (character_literal))))) name: (identifier) arguments: (argument_list))))) right: (decimal_integer_literal)))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (ternary_expression condition: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (string_literal) (string_literal)))))) consequence: (identifier) alternative: (string_literal)))))))