// editor5
import java.util.*;
public class Main
{
    public static void main(String[] args)
    {
        Scanner sc=new Scanner(System.in);
        int pa=sc.nextInt();
        if(pa<0)
        {
            System.out.print("Invalid input");
            return;
        }
        int term=sc.nextInt();
        if(term<1)
        {
            System.out.print("-1");
            return;
        }
        double rate=0.05;
        if(term<12)
        {
            double interest=(double)pa*rate*term;
        }
        else
        {
            double interest=(double)pa*rate;
        }
        System.out.printf("%.2f%n",interest);
    }
}