public static void main ( String [ ] args ) {
  Scanner input = new Scanner ( System . in ) ;
  int p = input . nextInt ( ) ;
  int n = input . nextInt ( ) ;
  boolean [ ] freq = new boolean [ 301 ] ;
  int result = - 1 ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    int num = input . nextInt ( ) ;
    int h = num % p ;
    if ( freq [ h ] ) {
      result = i + 1 ;
      break ;
    }
    freq [ h ] = true ;
  }
  System . out . println ( result ) ;
}

public static void main ( String [ ] args ) { Scanner input = new Scanner ( System . in ) ; int p = input . nextInt ( ) ; int n = input . nextInt ( ) ; boolean [ ] freq = new boolean [ 301 ] ; int result = - 1 ; for ( int i = 0 ; i < n ; i ++ ) { int num = input . nextInt ( ) ; int h = num % p ; if ( freq [ h ] ) { result = i + 1 ; break ; } freq [ h ] = true ; } System . out . println ( result ) ; }
(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: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (array_type element: (boolean_type) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (array_creation_expression type: (boolean_type) dimensions: (dimensions_expr (decimal_integer_literal))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (unary_expression operand: (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: (identifier)) update: (update_expression (identifier)) body: (block (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: (integral_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (identifier) right: (identifier)))) (if_statement condition: (parenthesized_expression (array_access array: (identifier) index: (identifier))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (identifier) right: (decimal_integer_literal)))) (break_statement))) (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (true))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier))))))