public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  boolean flag = true ;
  if ( n % 2 == 0 ) {
    flag = false ;
  }
  int [ ] arr = new int [ n ] ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    arr [ i ] = sc . nextInt ( ) ;
  }
  Arrays . sort ( arr ) ;
  double area = 0 ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    if ( flag ) {
      if ( i == 0 ) {
        area += Math . PI * arr [ i ] * arr [ i ] * 1d ;
      }
      else {
        area += Math . PI * arr [ i ] * arr [ i ] * 1d - Math . PI * arr [ i - 1 ] * arr [ i - 1 ] * 1d ;
      }
    }
    flag = ! flag ;
  }
  System . out . println ( area ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; boolean flag = true ; if ( n % 2 == 0 ) { flag = false ; } int [ ] arr = new int [ n ] ; for ( int i = 0 ; i < n ; i ++ ) { arr [ i ] = sc . nextInt ( ) ; } Arrays . sort ( arr ) ; double area = 0 ; for ( int i = 0 ; i < n ; i ++ ) { if ( flag ) { if ( i == 0 ) { area += Math . PI * arr [ i ] * arr [ i ] * 1d ; } else { area += Math . PI * arr [ i ] * arr [ i ] * 1d - Math . PI * arr [ i - 1 ] * arr [ i - 1 ] * 1d ; } } flag = ! flag ; } 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: (boolean_type) declarator: (variable_declarator name: (identifier) value: (true))) (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: (false))))) (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))))) (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)))) (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 (if_statement condition: (parenthesized_expression (identifier)) consequence: (block (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (binary_expression left: (binary_expression left: (field_access object: (identifier) field: (identifier)) right: (array_access array: (identifier) index: (identifier))) right: (array_access array: (identifier) index: (identifier))) right: (decimal_floating_point_literal))))) alternative: (block (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (binary_expression left: (binary_expression left: (binary_expression left: (field_access object: (identifier) field: (identifier)) right: (array_access array: (identifier) index: (identifier))) right: (array_access array: (identifier) index: (identifier))) right: (decimal_floating_point_literal)) right: (binary_expression left: (binary_expression left: (binary_expression left: (field_access object: (identifier) field: (identifier)) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal)))) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal)))) right: (decimal_floating_point_literal))))))))) (expression_statement (assignment_expression left: (identifier) right: (unary_expression operand: (identifier)))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier))))))