package yukicoder314;
import java.util.Scanner;
public class Main {
	public static void main(String[] args){
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
		long[] dp=new long[n+1];
		dp[0]=0;///ケン・ケン・パ　ケン・パ
		dp[1]=0;
		if(n==1){
			System.out.println(1);
			return;
		}
		dp[2]=1;
		if(n==2){
			System.out.println(2);
			return;
		}
		dp[3]=1;
		if(n==3){
			System.out.println(2);
			return;
		}
		for(int i=4;i<=n;i++){
			dp[i]=dp[i-2]+dp[i-3];
		}
		System.out.println(dp[n]+dp[n-1]+dp[n-2]);
	}
}