using System;

public class Program

{

    public static void Main()

    {

    int i, n;

    float tong = 0; 

    Console.Write("Nhap n: ");

    n = int.Parse(Console.ReadLine());

    i = 1;  

        while (i<=n)

        {

            tong = tong + 1.0f/(2*i);

            i++;

        }   

​

    Console.Write("Tong la: {0}",tong*1.0);

    }

}