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

public class Main {

    public static BigInteger[] f=new BigInteger[2005];

    public static BigInteger gcd(BigInteger a, BigInteger b)
    {
        while (!b.equals(BigInteger.ZERO))
        {
            BigInteger tmp=a.mod(b);
            a=b;
            b=tmp;
        }
        return a;
    }
    public static void println(Object x)
    {
        System.out.println(x);
    }


    public static void main(String arg[])
    {
        f[0]=new BigInteger("1");
        f[1]=new BigInteger("1");
        for (int i=2;i<2005;++i)
        {
            f[i]=new BigInteger("0");
            f[i]=f[i].add(f[i-1]).add(f[i-2]);
        }
        Scanner cin=new Scanner(System.in);
        String str;
        try {
            while ((str = cin.nextLine()) != null) {
                if (str.equals("") || str.equals("EOF")) break;
                int T = Integer.valueOf(str);
                println(f[T]);
            }
        }catch (Exception e)
        {

        }
    }
}