import java.math.BigInteger;
import java.util.Scanner;

public class Main{
    public static void main(String[] args) {
        Scanner in=new Scanner(System.in);
        BigInteger arr[]=new BigInteger[10000];
        arr[1]=BigInteger.ONE;
        arr[2]=new BigInteger("2");
        for(int i=3;i<arr.length;i++){
            arr[i]=arr[i-1].add(arr[i-2]);
        }
        while(in.hasNext()){
            int n=in.nextInt();
            System.out.println(arr[n]);
        }
    }
}