using System;

public class Program

{

    public static void Main()

    {

        double[] money = new double[5];

        int[] km = new int[5];

        for (int i = 0; i <= 4; i++)

        {

            money[i] = double.Parse(Console.ReadLine());

            km[i] = int.Parse(Console.ReadLine());

        }

        Console.WriteLine(money[4] * km[4]);

    }

}