import java.util.Scanner;

public class Main {
	static boolean memo[];
	static int ans, min;

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