import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {

    public static int getStep(int count) {
        if (count == 1) return 1;
        if (count == 2) return 2;

        return getStep(count - 1) + getStep(count - 2);
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int count = in.nextInt();
        int mt1 = 1;
        int mt2 = 2;

        if (count == 1 || count == 2) {
            System.out.println(count);
            return ;
        }


        for (int i = 3; i <= count; i++) {
            int temp = mt2;

            mt2 = mt1 + mt2;
            mt1 = temp;
        }

        System.out.println(mt2);
        // 注意 hasNext 和 hasNextLine 的区别
        // while (in.hasNextInt()) { // 注意 while 处理多个 case
        //     int a = in.nextInt();
        //     int b = in.nextInt();
        //     System.out.println(a + b);
        // }
    }
}