using System;

namespace Dragons_Hatching
{
    class Program
    {
        static void Main(string[] args)
        {
            int teams = int.Parse(Console.ReadLine());
            double dragonsHatchingValue = double.Parse(Console.ReadLine());
            double sum = 0;

            for (int i = 0; i < teams; i++)
            {
                string[] input = Console.ReadLine().Split(' ');
                long dragonsHatched = long.Parse(input[0]);
                long teamMembersCount = long.Parse(input[1]);
                double teamPoints = (double)dragonsHatched / teamMembersCount;
                sum += teamPoints;
            }
            double result = sum / dragonsHatchingValue;
            Console.WriteLine($"{result:f3}");
        }
    }
}