uva1646

//package uva1646;

import java.math.*;
import java.io.*;
import java.util.*;

public class Main {
	public static void main(String[] args){
		Scanner cin = new Scanner(new BufferedInputStream(System.in));
		
		BigInteger[] f = new BigInteger[10001];
		f[3] = BigInteger.valueOf(4);
		f[4] = BigInteger.valueOf(7);
		for (int i = 5; i <= 10000; ++i){
			f[i] = f[i-1].add(f[i-2]);
		}	
		
		int N;
		while (cin.hasNext()){
			N = cin.nextInt();
			System.out.println(f[N]);
		}
	}
}