import java.util.Scanner;

public class Fibonaci {

    private static long[] memory;
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        int n =Integer.parseInt(scanner.nextLine());
        memory=new long[n+1];
        long result=fibonaci( n);
        System.out.println(result);


    }

    private static long fibonaci(int n) {
        if (n<2) {
            return 1;

        }
        if(memory[n]!=0){
            return memory[n];
        }

        return   memory[n]   =fibonaci(n-1)+fibonaci(n-2);

    }
}