input: Write a function to calculate the nth term of the Fibonacci series. If the given input is less than 0, return -1.
  assert (nthFibonacciTerm(5)==3)
  assert (nthFibonacciTerm(10)==34)
  assert (nthFibonacciTerm(-3)==-1)
output: def nthFibonacciTerm(n):
      if n < 0:
          return -1
      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