The famous Fibonacci sequence: 1,1,2,3,5,8,13,21,34,55... If you carefully observe the sequence, what is the 11th number? What is the rule?

The famous Fibonacci sequence: 1,1,2,3,5,8,13,21,34,55... If you carefully observe the sequence, what is the 11th number? What is the rule?

The last number is the sum of its first two numbers (starting from the third number)
Fill in 89