public static void main ( String [ ] args ) {
  Scanner scan = new Scanner ( System . in ) ;
  int a = scan . nextInt ( ) ;
  double ans = 3.1415926535897932384626433832795028841971693993751058209 ;
  double ans2 = 0 ;
  int c [ ] = new int [ a ] ;
  for ( int i = 0 ;
  i != a ;
  i ++ ) {
    c [ i ] = scan . nextInt ( ) ;
  }
  Arrays . sort ( c ) ;
  for ( int i = 0 ;
  i != a ;
  i ++ ) {
    if ( i % 2 == 0 ) {
      ans2 += c [ i ] * c [ i ] ;
    }
    else {
      ans2 -= c [ i ] * c [ i ] ;
    }
  }
  ans *= ans2 ;
  if ( ans <= 0 ) {
    System . out . println ( ans * - 1 ) ;
  }
  else if ( ans > 0 ) {
    System . out . println ( ans ) ;
  }
}

public static void main ( String [ ] args ) { Scanner scan = new Scanner ( System . in ) ; int a = scan . nextInt ( ) ; double ans = 3.1415926535897932384626433832795028841971693993751058209 ; double ans2 = 0 ; int c [ ] = new int [ a ] ; for ( int i = 0 ; i != a ; i ++ ) { c [ i ] = scan . nextInt ( ) ; } Arrays . sort ( c ) ; for ( int i = 0 ; i != a ; i ++ ) { if ( i % 2 == 0 ) { ans2 += c [ i ] * c [ i ] ; } else { ans2 -= c [ i ] * c [ i ] ; } } ans *= ans2 ; if ( ans <= 0 ) { System . out . println ( ans * - 1 ) ; } else if ( ans > 0 ) { System . out . println ( ans ) ; } }
(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: (floating_point_type) declarator: (variable_declarator name: (identifier) value: (decimal_floating_point_literal))) (local_variable_declaration type: (floating_point_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) dimensions: (dimensions) 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)))) (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 (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: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (identifier)))))) alternative: (block (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (identifier))))))))) (expression_statement (assignment_expression left: (identifier) right: (identifier))) (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (unary_expression operand: (decimal_integer_literal))))))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier)))))))))