import java.util.*;
class Speed
{
    double acc;
    double time;
    double speed;
    
Speed( double a, double t)
{
    acc=a;
    time=t;
    speed=0.5*a*(t*t);
}
void print()
{
    System.out.printf("%.2f",speed);
}

}
class Main
{
    public static void main(String args[])
    {
    Scanner s=new Scanner(System.in);
    if(!hasNextDouble)
    {
        System.out.println("Invalid input");
        return;
    }
    double a=s.nextDouble();
    double t=s.nextDouble();
    
    Speed ob=new Speed(a,t);
    ob.print();
}
}