import java.util.*;

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]=dp[1]=1;
        for(int i=2; i<=N; i++){
            dp[i]=dp[i-1]+dp[i-2];
        }
        System.out.println(dp[N]);
    }
}