using System;

public class Hello
{
    public static void Main()
    {
        var n = int.Parse(Console.ReadLine().Trim());
        Console.WriteLine(getAns(n));
    }
    public static long getAns(int n)
    {
        if (n == 2) return 2;
        var dp = new long[n + 1];
        dp[1] = 1; dp[2] = 2;
        for (int i = 3; i <= n; i++)
            dp[i] = dp[i - 1] + dp[i - 2];
        return dp[n];
    }
}