import java.util.Scanner;

class Main {
	public static void main (String[] args) {
	    Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
	    int[] F = new int[51];
	    F[0] = 0;
	    F[1] = 1;
	    F[2] = 1;
	    F[3] = 2;
	    F[4] = 3;
	    for(int i = 5; i <= n; i++) {
	       F[i] = F[i-2] + F[i-3] + F[i-4];
	    }
	    System.out.println(F[n]);
	}
}