public static void main ( String [ ] args ) {
  Scanner in = new Scanner ( System . in ) ;
  int a = in . nextInt ( ) , b = in . nextInt ( ) ;
  if ( a < b ) System . out . print ( - 1 ) ;
  else System . out . printf ( "%.10f" , 1.0 * ( a + b ) / ( 2.0 * ( ( a + b ) / ( 2 * b ) ) ) ) ;
}

public static void main ( String [ ] args ) { Scanner in = new Scanner ( System . in ) ; int a = in . nextInt ( ) , b = in . nextInt ( ) ; if ( a < b ) System . out . print ( - 1 ) ; else System . out . printf ( " % .10f " , 1.0 * ( a + b ) / ( 2.0 * ( ( a + b ) / ( 2 * b ) ) ) ) ; }
(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))) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))) consequence: (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (unary_expression operand: (decimal_integer_literal))))) alternative: (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal) (binary_expression left: (binary_expression left: (decimal_floating_point_literal) right: (parenthesized_expression (binary_expression left: (identifier) right: (identifier)))) right: (parenthesized_expression (binary_expression left: (decimal_floating_point_literal) right: (parenthesized_expression (binary_expression left: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))) right: (parenthesized_expression (binary_expression left: (decimal_integer_literal) right: (identifier))))))))))))))