public static void main ( String [ ] args ) {
  FastScanner input = new FastScanner ( ) ;
  String s = input . next ( ) ;
  int letter [ ] = new int [ 26 ] ;
  for ( int i = 0 ;
  i < s . length ( ) ;
  i ++ ) {
    if ( s . charAt ( i ) == 'a' ) {
      letter [ 0 ] ++ ;
    }
    else {
      for ( int j = 0 ;
      j < s . charAt ( i ) - 'a' ;
      j ++ ) {
        if ( letter [ j ] == 0 ) {
          System . out . println ( "NO" ) ;
          return ;
        }
      }
      letter [ s . charAt ( i ) - 'a' ] ++ ;
    }
  }
  System . out . println ( "YES" ) ;
}

public static void main ( String [ ] args ) { FastScanner input = new FastScanner ( ) ; String s = input . next ( ) ; int letter [ ] = new int [ 26 ] ; for ( int i = 0 ; i < s . length ( ) ; i ++ ) { if ( s . charAt ( i ) == ' a ' ) { letter [ 0 ] ++ ; } else { for ( int j = 0 ; j < s . charAt ( i ) - ' a ' ; j ++ ) { if ( letter [ j ] == 0 ) { System . out . println ( " NO " ) ; return ; } } letter [ s . charAt ( i ) - ' a ' ] ++ ; } } System . out . println ( " YES " ) ; }
(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)))) (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) dimensions: (dimensions) value: (array_creation_expression type: (integral_type) dimensions: (dimensions_expr (decimal_integer_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: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list))) 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: (character_literal))) consequence: (block (expression_statement (update_expression (array_access array: (identifier) index: (decimal_integer_literal))))) alternative: (block (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) condition: (binary_expression left: (identifier) right: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal))) update: (update_expression (identifier)) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (decimal_integer_literal))) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal)))) (return_statement))))) (expression_statement (update_expression (array_access array: (identifier) index: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal))))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal))))))