Time Elapsed Since Last Boot (Exercise)

using System;
using System.Diagnostics;

class ConsoleTests
{
    static void Main()
    {
        var ticks = Stopwatch.GetTimestamp();
        var uptime = ((double)ticks) / Stopwatch.Frequency;
        var uptimeSpan = TimeSpan.FromSeconds(uptime);

        string output = null;
        output = "Last boot: " + uptimeSpan.ToString("%d") + " days, " + uptimeSpan.ToString("%h") +
            " hours, " + uptimeSpan.ToString("%m") + " minutes ago.";
        Console.WriteLine(output);
        Console.WriteLine();
        return;
    }
}