public static void Main()
Console.WriteLine("Enter units ");
int u=int.Parse(Console.ReadLine());
Console.WriteLine("payment is 0");
else if(u>=101 && u<=250)
Console.WriteLine("payment is "+(2*u+25));
else if(u>=251 && u<=450)
Console.WriteLine("payment is "+(4*u+75));
Console.WriteLine("payment is "+(6*u+100));