Solution for project euler problem 65

Problem 65

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Numerics;
using System.Text;

namespace Problem_65
{
    class Program
    {
        static void Main(string[] args)
        {
            Stopwatch sw = new Stopwatch();
            sw.Start();
            StringBuilder eFractionString = new StringBuilder();
            eFractionString.Append("2;1");
            for (int i = 2; i <= 66; i+=2)
                eFractionString.Append("," + i + ",1,1");
            List<Convergent> convergents = ConvergentsFromString(eFractionString.ToString());

            BigInteger sumOf100th = 0;
            BigInteger numeratorOf100th = convergents[99].Numerator;
            while (numeratorOf100th >= 10)
            {
                sumOf100th += numeratorOf100th%10;
                numeratorOf100th /= 10;
            }
            sumOf100th += numeratorOf100th;
            sw.Stop();
            Console.WriteLine(sumOf100th);
            Console.WriteLine("Took {0} ms.", sw.ElapsedMilliseconds);
            Console.ReadLine();

        }
        static List<Convergent> ConvergentsFromString(string s)
        {
            //accepts the format 2;1,2,3,4,5,6,7,8,9
            //dummy convergent to help in the calculation
            var convergents = new List<Convergent> {new Convergent {Numerator = 1, Denominator = 0}};
            BigInteger firstNumber = Int32.Parse(s.Substring(0, s.IndexOf(";")));
            convergents.Add(new Convergent {Numerator = firstNumber, Denominator = 1});

            s = s.Remove(0, s.IndexOf(";")+1);
            string[] parts = s.Split(new string[] {","}, StringSplitOptions.RemoveEmptyEntries);
            long[] multipliers = new long[parts.Length + 1];
            for (int i = 0; i < parts.Length; i++)
                multipliers[i + 1] = Int32.Parse(parts[i]);

            for (int i = 2; i <= multipliers.Length; i++)
            {

                BigInteger numerator = convergents[i - 1].Numerator*multipliers[i - 1] + convergents[i - 2].Numerator;
                BigInteger denominator = convergents[i - 1].Denominator*multipliers[i - 1] + convergents[i - 2].Denominator;
                convergents.Add(new Convergent {Numerator = numerator, Denominator = denominator});
            }
            convergents.RemoveAt(0);
            return convergents;
        }

        struct Convergent
        {
            public BigInteger Numerator;
            public BigInteger Denominator;
        }
    }
}