public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  String s = sc . next ( ) ;
  int max = 0 ;
  for ( int i = 1 ;
  i < n - 1 ;
  i ++ ) {
    int count = 0 ;
    for ( char c = 'a' ;
    c <= 'z' ;
    c ++ ) {
      if ( s . substring ( 0 , i ) . contains ( String . valueOf ( c ) ) && s . substring ( i ) . contains ( String . valueOf ( c ) ) ) {
        count ++ ;
      }
    }
    if ( count > max ) {
      max = count ;
    }
  }
  System . out . println ( max ) ;
  sc . close ( ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; String s = sc . next ( ) ; int max = 0 ; for ( int i = 1 ; i < n - 1 ; i ++ ) { int count = 0 ; for ( char c = ' a ' ; c <= ' z ' ; c ++ ) { if ( s . substring ( 0 , i ) . contains ( String . valueOf ( c ) ) && s . substring ( i ) . contains ( String . valueOf ( c ) ) ) { count ++ ; } } if ( count > max ) { max = count ; } } System . out . println ( max ) ; sc . close ( ) ; }
(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)))) (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: (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: (binary_expression left: (identifier) right: (decimal_integer_literal))) update: (update_expression (identifier)) body: (block (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: (character_literal))) condition: (binary_expression left: (identifier) right: (character_literal)) update: (update_expression (identifier)) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (decimal_integer_literal) (identifier))) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))))) right: (method_invocation object: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))))))) consequence: (block (expression_statement (update_expression (identifier))))))) (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (identifier))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier)))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))