import java.util.*;

public class Main {
    static long[] dp;
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
    	dp = new long[n + 1];
    	dp[0] = 1;
    	System.out.println(dfw(n));
    }
    
    static long dfw(int idx) {
        if (idx < 0) {
            return 0;
        }
        if (dp[idx] == 0) {
            dp[idx] = dfw(idx - 1) + dfw(idx - 2);
        }
        return dp[idx];
    }
}