help with loops

[cats_rule]

i need help with a program i am writing for college.
i dont want people to do it for me , im just after pointers & hints please.

the question is this

The user wants an application that allows her to enter a series of numbers until she decides to exit the application by typing 4 for quit. On starting the program the user should be asked to enter the first number. A menu should be displayed inviting the user to select an option from the menu.

Menu options include:
1. Add currently entered number to stored total and display new total
2. Subtract currently entered number from stored total and display new total
3. Average currently entered number with stored total, add to stored total and display new total
4. Quit the application and display the stored total

If the user types 4, the program should display “Goodbye”. Otherwise typing 1, 2 or 3 should ask the user to enter another number and display the result of the selected operation.

the code i have written so far is this

class Program
{
static void Main(string[] args)
{
double num1 = 0; // value of num1
double num2 = 0; // value of num2
double result = 0;
double temp; //value of temp
string enterFirst; // read enterFirst
string enterNum; // read enterNum
string myInput = ""; // read myInput
int count = 0;

Console.WriteLine("Enter First Number:"); // enter value for enterNum1
enterFirst = Console.ReadLine(); // read enterNum1
num1 = double.Parse(enterFirst);


while (myInput != "4")
{
Console.WriteLine("\n1. Add Numbers\n"); //display output
Console.WriteLine("\n2. Subtract Numbers\n"); //display output
Console.WriteLine("\n3.Average Numbers\n"); //display output
Console.WriteLine("\n4. Quit\n"); // display output
Console.WriteLine("\nPick option"); // display output
myInput = Console.ReadLine(); // read myInput

if (myInput == "4")
{
Console.WriteLine("Goodbye");
Console.WriteLine("The result is " + result);
}
else
{
Console.WriteLine("Enter a number");
enterNum = Console.ReadLine();
num2 = double.Parse(enterNum);

}
switch (myInput)
{

case "1": temp = num1 + num2;
count++;
if (count > 1)
{
temp = temp + num2;
result = temp;
}
break;

case "2": temp = num1 - num2;
count++;
if (count > 1)
{
temp = temp - num2;
result = temp;
}
break;
case "3":
break;
default:

break;
}
}
}

}

my problem is this ,
after the program loops round a second time im not sure how to get it to ignore the first entered number and just continue with the running total. Is this problem caused by using the switch statement, if not how can i over come this ??
any help is gratefully recieved , and rememebr only hint and tips please .
many thanks