Doug's submission

.gitignore

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+## Ignore Visual Studio temporary files, build results, and
+## files generated by popular Visual Studio add-ons.
+
+# User-specific files
+*.suo
+*.user
+*.sln.docstates
+
+# Build results
+
+[Dd]ebug/
+[Rr]elease/
+x64/
+[Bb]in/
+[Oo]bj/
+
+# MSTest test Results
+[Tt]est[Rr]esult*/
+[Bb]uild[Ll]og.*
+
+*_i.c
+*_p.c
+*_i.h
+*.ilk
+*.meta
+*.obj
+*.pch
+*.pdb
+*.pgc
+*.pgd
+*.rsp
+*.sbr
+*.tlb
+*.tli
+*.tlh
+*.tmp
+*.tmp_proj
+*.log
+*.vspscc
+*.vssscc
+.builds
+*.pidb
+*.log
+*.svclog
+*.scc
+
+# Visual C++ cache files
+ipch/
+*.aps
+*.ncb
+*.opensdf
+*.sdf
+*.cachefile
+
+# Visual Studio profiler
+*.psess
+*.vsp
+*.vspx
+
+# Guidance Automation Toolkit
+*.gpState
+
+# ReSharper is a .NET coding add-in
+_ReSharper*/
+*.[Rr]e[Ss]harper
+*.DotSettings.user
+
+# Click-Once directory
+publish/
+
+# Publish Web Output
+*.Publish.xml
+*.pubxml
+*.azurePubxml
+
+# NuGet Packages Directory
+## TODO: If you have NuGet Package Restore enabled, uncomment the next line
+packages/
+## TODO: If the tool you use requires repositories.config, also uncomment the next line
+!packages/repositories.config
+
+# Windows Azure Build Output
+csx/
+*.build.csdef
+
+# Windows Store app package directory
+AppPackages/
+
+# Others
+sql/
+*.Cache
+ClientBin/
+[Ss]tyle[Cc]op.*
+![Ss]tyle[Cc]op.targets
+~$*
+*~
+*.dbmdl
+*.[Pp]ublish.xml
+
+*.publishsettings
+
+# RIA/Silverlight projects
+Generated_Code/
+
+# Backup & report files from converting an old project file to a newer
+# Visual Studio version. Backup files are not needed, because we have git ;-)
+_UpgradeReport_Files/
+Backup*/
+UpgradeLog*.XML
+UpgradeLog*.htm
+
+# SQL Server files
+App_Data/*.mdf
+App_Data/*.ldf
+
+# =========================
+# Windows detritus
+# =========================
+
+# Windows image file caches
+Thumbs.db
+ehthumbs.db
+
+# Folder config file
+Desktop.ini
+
+# Recycle Bin used on file shares
+$RECYCLE.BIN/
+
+# Mac desktop service store files
+.DS_Store
+
+_NCrunch*

Program.cs

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+File.ReadLines(args[0]).ToList().ForEach(l=>Console.WriteLine(l.PadLeft(4,'0').Select((c,i)=>(c,i)).Aggregate("",(a,v)=>a+",M,MM,MMM,MMMM,MMMMM,,,,|,C,CC,CCC,CD,D,DC,DCC,DCCC,CM|,X,XX,XXX,XL,L,LX,LXX,LXXX,XC|,I,II,III,IV,V,VI,VII,VIII,IX".Split('|').Select(s=>s.Split(',')).ToArray()[v.i][v.c-48])));

code_golf_doug.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net9.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

code_golf_doug.sln

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+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.5.2.0
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "code_golf_doug", "code_golf_doug.csproj", "{47AACB49-BF7C-1A6B-2E23-4E8D738C0871}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{47AACB49-BF7C-1A6B-2E23-4E8D738C0871}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{47AACB49-BF7C-1A6B-2E23-4E8D738C0871}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{47AACB49-BF7C-1A6B-2E23-4E8D738C0871}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{47AACB49-BF7C-1A6B-2E23-4E8D738C0871}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {47F8AF99-7222-4ABA-A6D7-492B091D55C9}
+	EndGlobalSection
+EndGlobal