import java.util.Scanner;

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