import java.util.*;

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