import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.Scanner;

public class dpF {
    public static void main(String[] args) throws FileNotFoundException {
	Scanner in = new Scanner(new File("input.txt"));
        PrintWriter out = new PrintWriter(new File("output.txt"));
        int N = in.nextInt();
        BigInteger[] kol = new BigInteger[N+2];
        kol[0] = BigInteger.ONE;
        kol[1] = BigInteger.ONE;
        for (int i = 2; i <=N+1 ; i++) {
	    kol[i] = new BigInteger("0");

            kol[i] = kol[i].add(kol[i-1]);
            kol[i] = kol[i].add(kol[i-2]);

        }
        out.println(kol[N+1]);
        out.close();
    }
}