find the standard deviation of all keys in a map in csharp

main.cs
using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        // create a map
        Dictionary<int, string> map = new Dictionary<int, string>();
        map.Add(1, "one");
        map.Add(2, "two");
        map.Add(3, "three");
        map.Add(4, "four");
        map.Add(5, "five");

        // get an array of all the keys
        int[] keys = map.Keys.ToArray();

        // calculate the standard deviation
        double stdDev = keys.StandardDeviation();

        Console.WriteLine("Standard deviation of keys: {0}", stdDev);
    }
}

// extension method to calculate standard deviation of a sequence
public static class EnumerableExtensions
{
    public static double StandardDeviation(this IEnumerable<int> values)
    {
        double average = values.Average();
        double sumOfSquares = values.Sum(val => Math.Pow(val - average, 2));
        double result = Math.Sqrt(sumOfSquares / values.Count());
        return result;
    }
}
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