Find highest,lowest and average in a loop

I know it's probably something small that I'm doing wrong. I want it to print the lowest number etc. at the end of the loop, but it always prints zero as lowest. How do I get it to not put the exit mechanism zero as the lowest number.

Any advice please?

class HighLowAve
{
    public static void main (String[]args)
    {
        int num =0;
        int sum;
        int highest;
        int lowest;
        int index;
        Double average;

        highest = num;
        lowest = num;
        sum = 0;
        index = 0;

        do
        {
            System.out.println("Enter a number. Press zero to quit ");
            num = EasyIn.getInt();

            if (num > highest)
            {
                highest = num;
            }
            else if (num < lowest) 
            {
                lowest = num;
            }

            sum = sum + num;
            index++;
        }while (num !=0);

        average = (double) sum/(index-1);

        System.out.println("The highest number was " + highest);
        System.out.println("The lowest number was " + lowest);
        System.out.println("The average number was " + average);            
    }
}