C/C++ :: Take In Unsigned Number And Afterwards Return N-th Member Of Recursive Function

I'm having an issue with the following assignment:

Program is supposed to take in an unsigned number and afterwards return the 'n-th' member of the following recursive function:

f(1) = 1, f(2) = 2; f(3) = 3; f(n+3) = f(n+2) + f(n+1) + f(n), n>0;

When I worked with Fibonacci it was pretty easy since I just had to decrement the next member for each step. I used the following:

#include <stdio.h>
#include <stdlib.h>
#define MAX 100
int fib(int n) {
static int memorize[MAX] = {1,1};
if(memorize[n])
return memorize[n];

[Code] ....

My main problem is that I have no visual of the current function, as well as the fact that it takes the f(n+3) = f(n+2) + f(n+1) + f(n), whilist I've only got f(n) to begin with.