public static void main ( String [ ] args ) throws Exception {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  String po = sc . nextLine ( ) ;
  po = sc . nextLine ( ) ;
  int count = 0 ;
  for ( int i = 1 ;
  i < po . length ( ) ;
  i ++ ) {
    int nm = 0 ;
    String a = po . substring ( 0 , i ) ;
    String b = po . substring ( i ) ;
    Map < String , Integer > m = new HashMap < String , Integer > ( ) ;
    for ( int j = 0 ;
    j < a . length ( ) ;
    j ++ ) {
      m . put ( a . substring ( j , j + 1 ) , 1 ) ;
    }
    for ( int j = 0 ;
    j < b . length ( ) ;
    j ++ ) {
      if ( m . get ( b . substring ( j , j + 1 ) ) != null ) {
        nm ++ ;
        m . put ( b . substring ( j , j + 1 ) , null ) ;
      }
    }
    count = Math . max ( count , nm ) ;
  }
  System . out . println ( count ) ;
}

public static void main ( String [ ] args ) throws Exception { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; String po = sc . nextLine ( ) ; po = sc . nextLine ( ) ; int count = 0 ; for ( int i = 1 ; i < po . length ( ) ; i ++ ) { int nm = 0 ; String a = po . substring ( 0 , i ) ; String b = po . substring ( i ) ; Map < String , Integer > m = new HashMap < String , Integer > ( ) ; for ( int j = 0 ; j < a . length ( ) ; j ++ ) { m . put ( a . substring ( j , j + 1 ) , 1 ) ; } for ( int j = 0 ; j < b . length ( ) ; j ++ ) { if ( m . get ( b . substring ( j , j + 1 ) ) != null ) { nm ++ ; m . put ( b . substring ( j , j + 1 ) , null ) ; } } count = Math . max ( count , nm ) ; } System . out . println ( count ) ; }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (array_type element: (type_identifier) dimensions: (dimensions)) name: (identifier))) (throws (type_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)))) (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (expression_statement (assignment_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (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 (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (decimal_integer_literal) (identifier))))) (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))))) (local_variable_declaration type: (generic_type (type_identifier) (type_arguments (type_identifier) (type_identifier))) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (generic_type (type_identifier) (type_arguments (type_identifier) (type_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: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list))) update: (update_expression (identifier)) body: (block (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (binary_expression left: (identifier) right: (decimal_integer_literal)))) (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 (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (binary_expression left: (identifier) right: (decimal_integer_literal)))))) right: (null_literal))) consequence: (block (expression_statement (update_expression (identifier))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (binary_expression left: (identifier) right: (decimal_integer_literal)))) (null_literal)))))))) (expression_statement (assignment_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (identifier))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier))))))