import java.util.Scanner;

public class RecursiveFibonacci {
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);

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

        int[]numbers=new int[n];
        int []masiv=new int[numbers.length];

        //for (int i = 0; i <n ; i++) {
        if (n>=1 && n<=50) {
            numbers[0] = 1;
            numbers[1] = 1;
            for (int j = numbers[1] + 1; j < numbers.length; j++) {
                numbers[j] = numbers[j - 1] + numbers[j - 2];
            }
        }

       // }
        System.out.println(numbers[numbers.length-1]);
    }
}