public class Main{
	public static long array[] = new long[61];
	public static long num_of_ways(int n){
		if(array[n] == 0) {
			array[n] = num_of_ways(n-1) + num_of_ways(n-2) + num_of_ways(n-3);
        	return array[n];
    	}
		else {
        	return array[n];
    	}
	}
	public static void main (String[] args) throws java.lang.Exception 	{
		java.util.Scanner i = new java.util.Scanner(System.in);
		int n = i.nextInt();
		array[0] = 1;
    	array[1] = 1;
    	array[2] = 2;
		System.out.print(num_of_ways(n));
	}
}