using System;

public class Program

{

    static float Max(float[] grades){

        float max = grades[0];

        foreach(var el in grades)

        {

                    // if el > max, max = el 

        }

        return max;

    }

    static float Min(float[] grades){

        float min = grades[0];

        foreach(var el in grades)

        {

                    // if el < min, min = el 

​

        }

        return min;

    }

    static float Avg(float[] grades){

        float sum = 0;

        foreach(var el in grades)

        {

                    // add el to the sum

        }

        return sum / grades.Length;

    }

    public static void Main()

    {

        float[] grades = new float[]{ 13, 20, 17, 18.5f, 19, 10, 8 };

                Console.WriteLine("Highest grade: "+ Max(grades));

                Console.WriteLine("Lowest grade: "+ Min(grades));

                Console.WriteLine("Average grade: "+ Avg(grades));

    }

}