public static void main ( String args [ ] ) {
  Scanner s = new Scanner ( System . in ) ;
  int n = s . nextInt ( ) ;
  String str = s . next ( ) ;
  for ( int i = 1 ;
  i < n ;
  i ++ ) {
    if ( str . charAt ( i ) != str . charAt ( i - 1 ) ) {
      StringBuilder sb = new StringBuilder ( ) ;
      sb . append ( str . charAt ( i - 1 ) ) ;
      sb . append ( str . charAt ( i ) ) ;
      System . out . println ( "YES" ) ;
      System . out . println ( sb ) ;
      return ;
    }
  }
  System . out . println ( "NO" ) ;
}

public static void main ( String args [ ] ) { Scanner s = new Scanner ( System . in ) ; int n = s . nextInt ( ) ; String str = s . next ( ) ; for ( int i = 1 ; i < n ; i ++ ) { if ( str . charAt ( i ) != str . charAt ( i - 1 ) ) { StringBuilder sb = new StringBuilder ( ) ; sb . append ( str . charAt ( i - 1 ) ) ; sb . append ( str . charAt ( i ) ) ; System . out . println ( " YES " ) ; System . out . println ( sb ) ; return ; } } System . out . println ( " NO " ) ; }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (type_identifier) name: (identifier) dimensions: (dimensions))) 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)))) (local_variable_declaration type: (type_identifier) 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: (block (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (decimal_integer_literal)))))) consequence: (block (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (type_identifier) arguments: (argument_list)))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (decimal_integer_literal))))))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier)))))) (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 (identifier)))) (return_statement))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal))))))