import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long n = sc.nextInt();
        long[] dp = new long[3];
        dp[0] = 1;
        dp[1] = 1;
        int i;
        for (i = 2; i != n + 1; i++) {
            dp[i % 3] = dp[(i + 1) % 3] + dp[(i + 2) % 3];
        }
        System.out.println(dp[(i - 1) % 3]);

        sc.close();

    }
}