public static void main ( String [ ] args ) {
  FastReader sc = new FastReader ( ) ;
  long n = sc . nextInt ( ) ;
  long k = sc . nextInt ( ) ;
  long temp = Math . max ( n - 2 * k , 0 ) ;
  System . out . println ( ( n * ( n - 1 ) / 2 ) - ( temp * ( temp - 1 ) / 2 ) ) ;
}

public static void main ( String [ ] args ) { FastReader sc = new FastReader ( ) ; long n = sc . nextInt ( ) ; long k = sc . nextInt ( ) ; long temp = Math . max ( n - 2 * k , 0 ) ; System . out . println ( ( n * ( n - 1 ) / 2 ) - ( temp * ( temp - 1 ) / 2 ) ) ; }
(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)))) (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: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (binary_expression left: (decimal_integer_literal) right: (identifier))) (decimal_integer_literal))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (binary_expression left: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal)))) right: (decimal_integer_literal))) right: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal)))) right: (decimal_integer_literal)))))))))