Untitled

import java.util.*;

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