import java.util.*;
 

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int h = sc.nextInt();
		long[] dp = new long[51];
		dp[0]=1;
		dp[1]=1;
		for(int i=2;i<=50;i++){
			dp[i]=dp[i-1]+dp[i-2];
		}
		System.out.println(dp[h]);
	}
}