input: Write a function to generate the nth number in the Fibonacci sequence. If the input is 0, return 0. If the input is 1, return 1. For any other input, return the sum of the two preceding numbers in the sequence. 
  assert fibonacci_seq(0)==0
  assert fibonacci_seq(1)==1
  assert fibonacci_seq(5)==5
  assert fibonacci_seq(10)==55
output: def fibonacci_seq(n):
      if n == 0:
          return 0
      elif n == 1:
          return 1
      else:
          a, b = 0, 1
          for _ in range(2, n + 1):
              a, b = b, a + b
          return b