import java.util.Scanner;
import java.io.PrintWriter;
import java.io.IOException;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.math.BigInteger;
public class nunta{
    public static void main(String args[]) throws IOException{
        Scanner f = new Scanner(new FileInputStream ("nunta.in"));
        PrintWriter g= new PrintWriter(new FileOutputStream("nunta.out"));
        BigInteger A=new BigInteger("1");
        BigInteger B=new BigInteger("1");
        int n,i;
        n=f.nextInt();
        for(i=2;i<=n;++i) {
            B=(A=B).add(B);
        }
        g.write(B.toString());
        f.close();g.close();
    }
}