public static void main ( String [ ] args ) {
  Scanner s = new Scanner ( System . in ) ;
  String s1 = s . nextLine ( ) ;
  int k = s . nextInt ( ) ;
  HashMap < Character , Integer > h = new HashMap < > ( ) ;
  for ( int i = 0 ;
  i < s1 . length ( ) ;
  i ++ ) {
    if ( h . containsKey ( s1 . charAt ( i ) ) ) h . put ( s1 . charAt ( i ) , h . get ( s1 . charAt ( i ) ) + 1 ) ;
    else h . put ( s1 . charAt ( i ) , 1 ) ;
  }
  if ( k > s1 . length ( ) ) System . out . println ( "impossible" ) ;
  else if ( h . size ( ) >= k ) System . out . println ( "0" ) ;
  else {
    int count = k - h . size ( ) ;
    System . out . println ( count ) ;
  }
}

public static void main ( String [ ] args ) { Scanner s = new Scanner ( System . in ) ; String s1 = s . nextLine ( ) ; int k = s . nextInt ( ) ; HashMap < Character , Integer > h = new HashMap < > ( ) ; for ( int i = 0 ; i < s1 . length ( ) ; i ++ ) { if ( h . containsKey ( s1 . charAt ( i ) ) ) h . put ( s1 . charAt ( i ) , h . get ( s1 . charAt ( i ) ) + 1 ) ; else h . put ( s1 . charAt ( i ) , 1 ) ; } if ( k > s1 . length ( ) ) System . out . println ( " impossible " ) ; else if ( h . size ( ) >= k ) System . out . println ( "0" ) ; else { int count = k - h . size ( ) ; 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))) 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: (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: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (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)) 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 (if_statement condition: (parenthesized_expression (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier)))))) consequence: (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))))) right: (decimal_integer_literal))))) alternative: (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) (decimal_integer_literal))))))) (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) consequence: (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal)))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) right: (identifier))) consequence: (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal)))) alternative: (block (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier)))))))))