Please observe the law of the following numbers and fill in the appropriate numbers in brackets according to the law: 1,2,3,5,8,13,21, (), 55,89?

Please observe the law of the following numbers and fill in the appropriate numbers in brackets according to the law: 1,2,3,5,8,13,21, (), 55,89?

1,2,3,5,8,13,21,( 34),55,89.
Starting from the third, each is the sum of the first two