using System;

public class Hello
{
    static void Main()
    {
        var s = Console.ReadLine().Trim();
        getAns(s);
    }
    static void getAns(string s)
    {
        var n = s.Length;
        if (n % 3 != 0)
        {
            var w = n / 3;
            Console.WriteLine(w > 0 ? new string('9', w) : "0");
        }
        else
        {
            var w = n / 3;
            var ws = s.Substring(0, w);
            var ww = int.Parse(ws);
            var www = long.Parse(ws + ws + ws);
            var ww2 = w > 1 ? int.Parse(new string('9', w - 1)) : 0;
            var ans = ww + ww2;
            if (www > long.Parse(s)) ans--;
            Console.WriteLine(ans);
        }
    }
}