import java.util.ArrayDeque;
        import java.util.Deque;
        import java.util.Scanner;

public class Main {
    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        int number = Integer.parseInt(scanner.nextLine());

        getFibonacci(number);

    }

    private static void getFibonacci(int number) {
        Deque<Integer> stack = new ArrayDeque<>();
        if (number >= 0) {
            if (number == 0 || number == 1) {
                System.out.println(1);
                return;
            }

            int addend1 = 1;
            stack.push(addend1);
            int addend2 = 1;
            stack.push(addend2);

            for (int i = 1; i < number - 1; i++) {
                int tempAddend = addend1;
                addend1 = addend2;
                addend2 = tempAddend + addend2;

                stack.push(addend2);
            }

            int output = 0;
            output += stack.pop();
            output += stack.pop();
            System.out.println(output);
        }
    }
}