public static void main ( String [ ] args ) throws IOException {
  Scanner input = new Scanner ( System . in ) ;
  int n , b ;
  b = input . nextInt ( ) ;
  n = input . nextInt ( ) ;
  HashMap < Integer , Integer > map = new HashMap < > ( ) ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    int value = input . nextInt ( ) % b ;
    if ( map . containsKey ( value ) ) {
      System . out . println ( i + 1 ) ;
      return ;
    }
    else {
      map . put ( value , 1 ) ;
    }
  }
  System . out . println ( "-1" ) ;
}

public static void main ( String [ ] args ) throws IOException { Scanner input = new Scanner ( System . in ) ; int n , b ; b = input . nextInt ( ) ; n = input . nextInt ( ) ; HashMap < Integer , Integer > map = new HashMap < > ( ) ; for ( int i = 0 ; i < n ; i ++ ) { int value = input . nextInt ( ) % b ; if ( map . containsKey ( value ) ) { System . out . println ( i + 1 ) ; return ; } else { map . put ( value , 1 ) ; } } System . out . println ( " - 1" ) ; }
(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)) declarator: (variable_declarator name: (identifier))) (expression_statement (assignment_expression left: (identifier) right: (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: (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: (identifier)) update: (update_expression (identifier)) body: (block (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) right: (identifier)))) (if_statement condition: (parenthesized_expression (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier)))) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (decimal_integer_literal))))) (return_statement)) alternative: (block (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (decimal_integer_literal)))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal))))))