import java.util.Scanner;

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

        int Pamount = sc.nextInt(); // principal amount

        if (Pamount < 0) {
            System.out.println("Invalid input");
            return;
        }

        int time = sc.nextInt(); // loan term in months

        if (time < 1) {
            System.out.println("-1");
            return;
        }

        double rate = 0.05 / 12; // 5% annual interest → monthly rate

        double interest = Pamount * rate * time;

        System.out.printf("%.2f\n", interest);
    }
}