--description--

Write a function to generate the <code>n^th</code> Fibonacci number.

The <code>n^th</code> Fibonacci number is given by:

<code>F_n = F_n-1 + F_n-2</code>

The first two terms of the series are 0 and 1.

Hence, the series is: 0, 1, 1, 2, 3, 5, 8, 13...

--hints--

fibonacci should be a function.

assert(typeof fibonacci === 'function');

fibonacci(2) should return a number.

assert(typeof fibonacci(2) == 'number');

fibonacci(3) should return 2.

assert.equal(fibonacci(3), 2);

fibonacci(5) should return 5.

assert.equal(fibonacci(5), 5);

fibonacci(10) should return 55.

assert.equal(fibonacci(10), 55);

--seed--

--seed-contents--

function fibonacci(n) {

}

--solutions--

function fibonacci(n) {
  let a = 0, b = 1, t;
  while (--n >= 0) {
    t = a;
    a = b;
    b += t;
  }
  return a;
}