import java.util.*;

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