import java.util.*;
public class Main{
    public static void main(String [] args){
        int a=0,b=1;
        Scanner sc= new Scanner(System.in);
        int n=sc.nextInt();         
            for(int i=1;i<n;i++){
                b+=a;
                a=b-a;
            }
        System.out.println(b);
    }
}