text: The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,
  
  F(0) = 0, F(1) = 1
  F(n) = F(n - 1) + F(n - 2), for n > 1.
  Given n, calculate F(n).
  
   
  
  Example 1:
  
  Input: n = 2
  Output: 1
  Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.
  Example 2:
  
  Input: n = 3
  Output: 2
  Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.
  Example 3:
  
  Input: n = 4
  Output: 3
  Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.
   
  
  Constraints:
  
  0 <= n <= 30
  
  Solution:-
    
    class Solution:
      def fib(self, n: int) -> int:
          if n==0:
              return 0
          if n==1:
              return 1
          ans=self.fib(n-1)+self.fib(n-2)
          return ans
  