public static void main ( String [ ] args ) throws IOException {
  FastReader fr = new FastReader ( ) ;
  PrintWriter pw = new PrintWriter ( System . out ) ;
  double X = fr . nextDouble ( ) / fr . nextDouble ( ) ;
  double Y = fr . nextDouble ( ) / fr . nextDouble ( ) ;
  double multiplier = ( 1 - X ) * ( 1 - Y ) ;
  double sum = X * ( 1 ) / ( 1 - multiplier ) ;
  pw . println ( sum ) ;
  pw . close ( ) ;
}

public static void main ( String [ ] args ) throws IOException { FastReader fr = new FastReader ( ) ; PrintWriter pw = new PrintWriter ( System . out ) ; double X = fr . nextDouble ( ) / fr . nextDouble ( ) ; double Y = fr . nextDouble ( ) / fr . nextDouble ( ) ; double multiplier = ( 1 - X ) * ( 1 - Y ) ; double sum = X * ( 1 ) / ( 1 - multiplier ) ; pw . println ( sum ) ; pw . close ( ) ; }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (array_type element: (type_identifier) dimensions: (dimensions)) name: (identifier))) (throws (type_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: (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: (floating_point_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list))))) (local_variable_declaration type: (floating_point_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list))))) (local_variable_declaration type: (floating_point_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (parenthesized_expression (binary_expression left: (decimal_integer_literal) right: (identifier))) right: (parenthesized_expression (binary_expression left: (decimal_integer_literal) right: (identifier)))))) (local_variable_declaration type: (floating_point_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (binary_expression left: (identifier) right: (parenthesized_expression (decimal_integer_literal))) right: (parenthesized_expression (binary_expression left: (decimal_integer_literal) right: (identifier)))))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier)))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))