Java Programming Question?

Here's my code. But why the hell doesn't this work? No compiler errors, so it must be an error on my part. Whenever I run it for some reason it omits the last value for the average. I ran it with the values: X= 100 miles traveled, 100 miles traveled, 100 miles traveled and Y= 5 gallons, 4 gallons, 10 gallons. When it calculates the average its not 18.33 like its supposed to be, its 15 like it omitted including the last value for each coord yet still divided it by 3? Help please?

import java.util.Scanner;

public class Mpgcalc {

/**

* @param args the command line arguments

*/

public static void main( String[] args )

{

// TODO code application logic here

Scanner input = new Scanner( System.in );

int miles;

int gallons;

int counter;

double total;

double average;

double mpg;

total = 0;

counter = 0;

System.out.print( "Enter miles traveled: ");

miles = input.nextInt();

System.out.print( "Enter amount of gallons used: ");

gallons = input.nextInt();

mpg = ( miles/gallons );

System.out.printf( "\nYour gas mileage for your trip was %.2f\n", mpg );

System.out.printf( "Enter miles traveled (or type -1 to stop adding \n additional values): ");

miles = input.nextInt();

while ( miles != -1 )

{

System.out.print( "Enter amount of gallons used: ");

gallons = input.nextInt();

mpg = ( miles / gallons );

System.out.printf( "\nYour gas mileage for your trip was %.2f\n", mpg );

System.out.printf( "Enter miles traveled (or type -1 to stop adding \n additional values): ");

miles = input.nextInt();

}

if ( counter != 0 )

{

average = ( total/counter );

System.out.printf( "\nTotal number of trips entered is %d\n", counter );

System.out.printf( "Average miles per gallon is %.2f\n", average );

}

else

System.out.println( "No input received from user. Program Terminating" );

}

}