import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author silviase
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        KyotoUniv solver = new KyotoUniv();
        solver.solve(1, in, out);
        out.close();
    }

    static class KyotoUniv {
        public void solve(int testNumber, Scanner in, PrintWriter out) {

            int n = in.nextInt();
            long[] a = new long[n + 2];
            a[0] = 1;
            for (int i = 0; i < n; i++) {
                a[i + 1] += a[i];
                a[i + 2] += a[i];
            }

            out.println(a[n]);
        }

    }
}