import java.util.*;
import java.awt.geom.*;
import java.io.*;
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		long[] dp = new long[N+1];
		dp[0] = 1;
		for(int i = 0; i < N; i++) {
			dp[i+1] += dp[i];
			if(i + 2 <= N) dp[i+2] += dp[i];
		}
		System.out.println(dp[N]);
 	}
}