import java.util.Scanner;

public class No44 {
    public static void main(String[] args){
        int N;
        Scanner sc = new Scanner(System.in);
        N = sc.nextInt();
        
        long[] combination = new long[N+1];
        combination[0] = 1;
        combination[1] = 1;
        for(int i=2; i<N+1; i++){
            combination[i] = combination[i-1] + combination[i-2];
        }
        System.out.println(combination[N]);
    }
}