<s>[INST] A person has a choice of 4 highway routes from City A to City B. From City B she has a choice of 3 routes to City C. From City C she has a choice of 2 routes to City D. Approach this problem recursively and define a function f(n) that represents the number of routes available from City A to City D. Although not necessary, you can define other functions g and h if it makes the solution clearer.[/INST]