import java.util.Scanner;


public class Main_yukicoder44 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        long[] dp = new long[n + 2];
        dp[0] = 1;

        for (int i = 0; i < n; i++) {
        	dp[i + 2] += dp[i];
        	dp[i + 1] += dp[i];
        }
        
        System.out.println(dp[n]);

        sc.close();
    }
}