import java.util.Scanner;

public class FibNumbs {

	public static void main(String[] args) {

		Scanner input = new Scanner(System.in);
		System.out.println("Enter a number");

		int number = Integer.parseInt(input.nextLine());
		int f[] = new int[number + 2]; // 1 extra to handle case, n = 0
		int i;

		f[0] = 0;
		f[1] = 1;

		for (i = 2; i <= number; i++)
			f[i] = f[i - 1] + f[i - 2];

		System.out.println(f[number]);

	}

}