input: Write a function to generate the nth number in the Fibonacci sequence. The function should take an integer n as input and return the nth number in the sequence. If n is 0, the function should return 0. If n is 1, the function should return 1. For any other value of n, the function should return the sum of the (n-1)th and (n-2)th numbers in the sequence.
  assert fibonacci_seq(0)==0
  assert fibonacci_seq(1)==1
  assert fibonacci_seq(2)==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