Mathematics · Permutations and Combinations

Ankita has to climb 5 stairs starting at the ground, while respecting the following rules: 1. At any stage, Ankita can move either one or two stairs up. 2. At any stage, Ankita cannot move to a lower step. Let f(n) denote the number of possible ways in which Ankita can reach the n-th stair. For example, f(1) = 1, f(2) = 2, f(3) = 3. Find the value of f(5).