using System;
using System.Collections.Generic;

namespace y
{
    class Program
    {
        static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());
            var s = new List<int>();
            int a = 0;
            for (int i = 2; i <= n; i++)
            {
                if (s.Contains(i)) continue;
                else
                {
                    a += i;
                    int e = i;
                    int c = 2;
                    while (e * c <= n)
                    {
                        s.Add(e * c);
                        c++;
                    }
                }
            }

            Console.WriteLine(a);
        }
    }
}