using System;
public class Program
{
public static void Main()
Console.WriteLine(ReverseString("Hello World"));
}
public static string ReverseString(string str)
char[] chars = new char[str.Length];
for (int i = 0, j =str.Length - 1; i <= j; i++, j--)
chars[i] = str[j];
chars[j] = str[i];
return new string(chars);