too simple C# .NET program

/* The Computer Language Benchmarks Game
   https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
*/

class TooSimple {
public static void Main(String[] args) {   
    // mtime side-effect   
    using (FileStream fs = File.Create("./one")) { } 
      
    long n = Int64.Parse(args[0]);
    double sum = 0.0;
    double flip = -1.0;
    for (long i = 1; i <= n; i++) {    
        flip *= -1.0;        
        sum += flip / (2*i - 1);               
    }  
    Console.WriteLine("{0:f9}", sum*4.0);
    
    // mtime side-effect   
    using (FileStream fs = File.Create("./two")) { }     
}
}
    

NOTES:
64-bit Ubuntu quad core
.NET SDK 9.0.100
Host Version: 9.0.0
Commit: 9d5a6a9aa4

<OutputType>Exe
<TargetFramework>net9.0
<ImplicitUsings>enable
<Nullable>enable
<AllowUnsafeBlocks>true
<ServerGarbageCollection>true
<ConcurrentGarbageCollection>true
<PublishAot>false



 Wed, 13 Nov 2024 23:16:56 GMT

MAKE:
cp toosimple.csharpcore Program.cs
cp Include/csharpcore/program.csproj .
mkdir obj
cp Include/csharpcore/project.assets.json ./obj
/opt/src/dotnet-sdk-9.0.100/dotnet build -c Release --use-current-runtime  	
  Determining projects to restore...
/home/dunham/all-benchmarksgame/benchmarksgame_i53330/toosimple/tmp/program.csproj : warning NU1900: Error occurred while getting package vulnerability data: Unable to load the service index for source https://api.nuget.org/v3/index.json.
  Restored /home/dunham/all-benchmarksgame/benchmarksgame_i53330/toosimple/tmp/program.csproj (in 6.34 sec).
/home/dunham/all-benchmarksgame/benchmarksgame_i53330/toosimple/tmp/program.csproj : warning NU1900: Error occurred while getting package vulnerability data: Unable to load the service index for source https://api.nuget.org/v3/index.json.
  program -> /home/dunham/all-benchmarksgame/benchmarksgame_i53330/toosimple/tmp/bin/Release/net9.0/linux-x64/program.dll

Build succeeded.

/home/dunham/all-benchmarksgame/benchmarksgame_i53330/toosimple/tmp/program.csproj : warning NU1900: Error occurred while getting package vulnerability data: Unable to load the service index for source https://api.nuget.org/v3/index.json.
/home/dunham/all-benchmarksgame/benchmarksgame_i53330/toosimple/tmp/program.csproj : warning NU1900: Error occurred while getting package vulnerability data: Unable to load the service index for source https://api.nuget.org/v3/index.json.
    2 Warning(s)
    0 Error(s)

Time Elapsed 00:00:11.33

13.32s to complete and log all make actions

COMMAND LINE:
 ./bin/Release/net9.0/linux-x64/program 10000000000

PROGRAM OUTPUT:
3.141592653