#include <stdio.h>

int main()
{
	int n;
	while(scanf("%d",&n) != EOF)
	{
		if(n == 0 || n == 1) printf("1\n");
		else if(n == 2) printf("2\n");
		else
		{
			long long i,a = 1,b = 1,c = 2,t;
			for(i = 2; i < n; i++)
			{
				t = a+b+c;
				a = b;
				b = c;
				c = t;
			}
			printf("%lld\n",c);
		}
		
	}
	return 0;
}