using System;

public class Program

{

    public static void Main()

    {

        int Length;

Console.Write("Length: ");

while (true) {

    if(int.TryParse(Console.ReadLine(), out Length)) {

        if (Length > 0) {

            break;

        } else {

            Console.WriteLine("Invalid input");

            Console.Write("Length: ");

        }

    } else { 

        Console.WriteLine("Invalid input");

        Console.Write("Length: ");

    }

}

int width;

Console.Write("width: ");

while (true) {

    if (int.TryParse(Console.ReadLine(), out width)) {

        if (width > 0) {

            break;

        } else {

            Console.WriteLine("Invalid input");

            Console.Write("width: ");

        }

    } else {

        Console.WriteLine("Invalid input");

        Console.Write("width: ");

    }

}

int cost;

if (width * Length < 400) {

    cost = 25;

} else if (width * Length <600) {

    cost = 35;

} else {

    cost = 50;

}

Console.WriteLine($"We charge {cost:c} per week for that size lawn\nThat will cost you {cost*20:C} in total");

Console.Read();

    }

}