import java.util.Scanner;
public class Yuki44{
	public static void main(String[] arg){
		Scanner sc= new Scanner(System.in);
		int n;
		n = sc.nextInt();
		long[] dp = new long[n+1];
		dp[0] = 1;
		dp[1] = 1;
		for(int i = 2;i<n+1;i++){
			dp[i] = dp[i-1] + dp[i-2];
		}
		System.out.println(dp[n]);
	}
}