import java.math.*;
import java.util.*;
public class Main {

    public static void main(String[] args) {
        // TODO 自动生成的方法存根
        BigInteger [][] dp = new BigInteger[300][2];
        dp[1][1] = BigInteger.ONE;
        dp[1][0] = BigInteger.ZERO;
        for (int i=2;i<=200;i++) {
            dp[i][1] = dp[i-1][1].add(dp[i-1][0]);
            dp[i][0] = dp[i-1][1];
        }
        Scanner cin = new Scanner(System.in);
        int n;
        while(cin.hasNext()){
            n = cin.nextInt();
            System.out.println(dp[n][1].add(dp[n][0]));
        }

    }

}