RainDrops

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Raindrops
{
    class Program
    {
        static void Main(string[] args)
        {
            double region = double.Parse(Console.ReadLine());
            decimal density = decimal.Parse(Console.ReadLine());
            decimal result = 0;


            for (int i = 0; i < region; i++)
            {
                double[] input = Console.ReadLine().Split(' ').Select(x => double.Parse(x)).ToArray();
                double raindropsCount = input[0];
                double squareMeters = input[1];
                //Console.WriteLine(raindropsCount / squareMeters);
                result += (decimal)(raindropsCount / squareMeters);

            }

            try
            {
                Console.WriteLine("{0:F3}", result / density);
            }
            catch (Exception e)
            {

                Console.WriteLine("{0:F3}", result);
            }

        }
    }
}