$\mathbf{Algorithm}\ \Fib(n)\mathrm{:}$ $\mathbf{if}\ n = 0\ \mathrm{or}\ n = 1$ $\mathbf{then}\ f = n$ $\mathbf{else}\ f = \Fib(n - 1) + \Fib(n - 2)$ $\mathbf{endif};$ $\mathbf{return}\ f$