The Fibonacci sequence is a series where each number is the sum of the two preceding ones.

1. Using Iterative Approach:
   • Efficient and avoids the exponential time complexity of the recursive approach.
2. Code Example:
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   def fibonacci(n):
       if n <= 0:
           return "Invalid input"
       elif n == 1:
           return 0
       elif n == 2:
           return 1
       a, b = 0, 1
       for _ in range(2, n):
           a, b = b, a + b
       return b
   
   print(fibonacci(10))  # Output: 34
   

   Explanation:
   • The iterative approach calculates the Fibonacci number in O(n) time.
   • Handles edge cases for invalid input and small values of n.