Calculate the First 1,000-Digit Fibonacci Number C# with Example

Include using System.Numerics and add a reference to System.Numerics to the project. 
using System; 
using System.Numerics; 
namespace Euler_25 
{ 
class Program 
{ 
static void Main(string[] args) 
{ 
BigInteger l1 = 1; 
BigInteger l2 = 1; 
BigInteger current = l1 + l2; 
while (current.ToString().Length < 1000) 
{ 
l2 = l1; 
l1 = current; 
current = l1 + l2; 
} 
Console.WriteLine(current); 
} 
} 
} 
This simple algorithm iterates through Fibonacci numbers until it reaches one at least 1000 decimal digits in length, 
then prints it out. This value is significantly larger than even a ulong could hold. 
Theoretically, the only limit on the BigInteger class is the amount of RAM your application can consume. 
Note: BigInteger is only available in .NET 4.0 and higher.