import java.util.Arrays;
import java.util.LinkedList;
import java.util.Scanner;

public class Main {
	
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		final int N = sc.nextInt();
		
		long[] DP = new long[N + 1];
		DP[0] = 1;
		for(int cur = 0; cur < N; cur++){
			if(cur + 1 <= N){ DP[cur + 1] += DP[cur]; }
			if(cur + 2 <= N){ DP[cur + 2] += DP[cur]; }
		}
		
		System.out.println(DP[N]);
		
	}
	
}