Cake

import java.util.Scanner;

public class Cake {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        double l = Double.parseDouble(scanner.nextLine());
        double w = Double.parseDouble(scanner.nextLine());
        double volume = l * w;
        double result = 0;
        double pieces;

        //String str = " ";

        while (result <= volume) {

            double num = Double.parseDouble(scanner.nextLine());
            result += num;
            if (str.equals("STOP")){
                String str = scanner.nextLine();
                pieces = Math.abs(result - volume);
            }
        } pieces = Math.abs(result - volume);
        System.out.println(pieces);
    }
}