import java.io.;
import java.util.;
public class Main{
public static void main(String args[]) throws Exception{
Scanner cin = new Scanner(System.in);
var n = cin.nextInt();
System.out.println(f(n));
}
public static int f(int n){
if(n <= 2) return 1;
return f(n - 2) + f(n - 1);
}
}