public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  sc . nextLine ( ) ;
  String s = sc . nextLine ( ) ;
  int val = n / 2 ;
  char prev = '#' ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    char curr = s . charAt ( i ) ;
    if ( i == 0 ) {
      prev = curr ;
      continue ;
    }
    else if ( prev != curr ) {
      System . out . println ( "YES" ) ;
      System . out . println ( prev + "" + curr ) ;
      return ;
    }
    prev = curr ;
  }
  System . out . println ( "NO" ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; sc . nextLine ( ) ; String s = sc . nextLine ( ) ; int val = n / 2 ; char prev = ' # ' ; for ( int i = 0 ; i < n ; i ++ ) { char curr = s . charAt ( i ) ; if ( i == 0 ) { prev = curr ; continue ; } else if ( prev != curr ) { System . out . println ( " YES " ) ; System . out . println ( prev + " " + curr ) ; return ; } prev = curr ; } System . out . println ( " NO " ) ; }
(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: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (expression_statement (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)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (identifier) right: (decimal_integer_literal)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (character_literal))) (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: (block (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))))) (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (identifier))) (continue_statement)) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal)))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (binary_expression left: (binary_expression left: (identifier) right: (string_literal)) right: (identifier))))) (return_statement)))) (expression_statement (assignment_expression left: (identifier) right: (identifier))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal))))))