package yukicoder044;
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]=1;
		dp[1]=1;
		for(int i=2;i<=n;i++){
			dp[i]=dp[i-1]+dp[i-2];
		}
		System.out.println(dp[n]);
		sc.close();
	}	
}