2193.java

import java.util.*;

public class Main {

 public static void main(String[] args) {

 Scanner sc = new Scanner(System.in);

 int n = sc.nextInt();
 long[][] arr = new long[n+1][2];

 arr[1][1] = 1;

 for(int i=2; i<=n; i++) {
 arr[i][0] = arr[i-1][0] + arr[i-1][1];
 arr[i][1] = arr[i-1][0];
 }

 System.out.println(arr[n][0] + arr[n][1]);
 }
}