import java.util.Scanner;
public class fibonacci {

public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);

    int num = sc.nextInt();

    long[] array = new long[num+1]; //int 범위(2,147,483,647)를 초과 long으로 선언

    //고정되어있는 값대입
    array[0] = 0;
    array[1] = 1;

    for(int i=2; i< array.length; i++) {
        array[i] = array[i-1] + array[i-2];
    }

    System.out.println(array[num]);
    }
}