public static void main ( String [ ] args ) {
  Scanner scanner = new Scanner ( System . in ) ;
  int N = scanner . nextInt ( ) ;
  int [ ] radius = new int [ N ] ;
  double pi = Math . PI ;
  double area = 0 ;
  for ( int i = 0 ;
  i < N ;
  i ++ ) {
    radius [ i ] = scanner . nextInt ( ) ;
  }
  Arrays . sort ( radius ) ;
  for ( int i = N - 1 ;
  i >= 0 ;
  i -- ) {
    if ( N % 2 == 0 ) {
      if ( i % 2 == 0 ) {
        area -= pi * radius [ i ] * radius [ i ] ;
      }
      else if ( i % 2 == 1 ) {
        area += pi * radius [ i ] * radius [ i ] ;
      }
    }
    if ( N % 2 == 1 ) {
      if ( i % 2 == 0 ) {
        area += pi * radius [ i ] * radius [ i ] ;
      }
      else if ( i % 2 == 1 ) {
        area -= pi * radius [ i ] * radius [ i ] ;
      }
    }
  }
  System . out . println ( area ) ;
}

public static void main ( String [ ] args ) { Scanner scanner = new Scanner ( System . in ) ; int N = scanner . nextInt ( ) ; int [ ] radius = new int [ N ] ; double pi = Math . PI ; double area = 0 ; for ( int i = 0 ; i < N ; i ++ ) { radius [ i ] = scanner . nextInt ( ) ; } Arrays . sort ( radius ) ; for ( int i = N - 1 ; i >= 0 ; i -- ) { if ( N % 2 == 0 ) { if ( i % 2 == 0 ) { area -= pi * radius [ i ] * radius [ i ] ; } else if ( i % 2 == 1 ) { area += pi * radius [ i ] * radius [ i ] ; } } if ( N % 2 == 1 ) { if ( i % 2 == 0 ) { area += pi * radius [ i ] * radius [ i ] ; } else if ( i % 2 == 1 ) { area -= pi * radius [ i ] * radius [ i ] ; } } } System . out . println ( area ) ; }
(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: (array_type element: (integral_type) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (array_creation_expression type: (integral_type) dimensions: (dimensions_expr (identifier))))) (local_variable_declaration type: (floating_point_type) declarator: (variable_declarator name: (identifier) value: (field_access object: (identifier) field: (identifier)))) (local_variable_declaration type: (floating_point_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: (identifier)) update: (update_expression (identifier)) body: (block (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier)))) (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (identifier) right: (decimal_integer_literal)))) condition: (binary_expression left: (identifier) right: (decimal_integer_literal)) update: (update_expression (identifier)) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (block (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (binary_expression left: (identifier) right: (array_access array: (identifier) index: (identifier))) right: (array_access array: (identifier) index: (identifier)))))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (binary_expression left: (identifier) right: (array_access array: (identifier) index: (identifier))) right: (array_access array: (identifier) index: (identifier)))))))))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (block (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (binary_expression left: (identifier) right: (array_access array: (identifier) index: (identifier))) right: (array_access array: (identifier) index: (identifier)))))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (binary_expression left: (identifier) right: (array_access array: (identifier) index: (identifier))) right: (array_access array: (identifier) index: (identifier)))))))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier))))))