import java.util.*;

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