Sync folders by copying only new files, ignoring moved files on target path

app.config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup>
  <appSettings>
    <add key="FromPath" value="C:\ftpRoot\mySite1;C:\ftpRoot\mySite2"/>
    <add key="ToPath" value="C:\ToProcess\mySite1;C:\ToProcess\mySite2"/>
    <add key="LogPath" value="C:\ToProcess\transferLog.txt"/>
  </appSettings>
</configuration>

Program.cs

 class Program
    {
        static void Main(string[] args)
        {
            var fromPaths = ConfigurationManager.AppSettings["FromPath"].Split(';');
            var toPaths = ConfigurationManager.AppSettings["ToPath"].Split(';');

            if (fromPaths.Length != toPaths.Length)
            {
                throw new ApplicationException(string.Format("From paths must be equal to to paths. Got {0} from and {1} to", fromPaths.Length, toPaths.Length));
            }

            var logFile = ConfigurationManager.AppSettings["LogPath"];
            if (File.Exists(logFile))
            {
                File.Delete(logFile);
            }


            for (var folderIndex = 0; folderIndex < fromPaths.Length; folderIndex++) {
                var toPath = toPaths[folderIndex];
                var fromPath = fromPaths[folderIndex];
                if (!Directory.Exists(toPath))
                {
                    throw new ApplicationException(string.Format("toPath {0} not exists", toPath));
                }
                if (!Directory.Exists(fromPath))
                {
                    throw new ApplicationException(string.Format("fromPath {0} not exists", fromPath));
                }

                // We need to copy all filed in the root of from path to the 
                // location of toPath excluding the files that are not already in 
                // a subfolder of the toPath

                using (var log = File.AppendText(logFile)) {
                    log.WriteLine(String.Format("Processing files in folder {0}. Start on {1:dd/MM/yyyy hh:mm:ss}", fromPath, DateTime.Now));
                    var filesHashSet = new HashSet<string>();
                    GetListOfExistingFiles(toPath, filesHashSet);
                    log.WriteLine(String.Format("Found {0} existing files on {1:dd/MM/yyyy hh:mm:ss}", filesHashSet.Count, DateTime.Now));
                    foreach (var f in Directory.EnumerateFiles(fromPath, "*", SearchOption.TopDirectoryOnly))
                    {
                        var fileInfo = new FileInfo(f);
                        if (!filesHashSet.Contains(fileInfo.Name))
                        {
                            log.Write(String.Format("New file detected: {0} : ", fileInfo.Name));
                            fileInfo.CopyTo(Path.Combine(toPath, fileInfo.Name));
                            log.Write("Copied" + Environment.NewLine);
                        }
                    }
                    log.WriteLine(String.Format("Finished on {0:dd/MM/yyyy hh:mm:ss}", DateTime.Now));
                }
            }
        }

        private static void GetListOfExistingFiles(string toPath, HashSet<string> filesHashSet)
        {
            foreach (var f in Directory.EnumerateFiles(toPath, "*", SearchOption.AllDirectories))
            {
                var fileInfo = new FileInfo(f);
                if (!filesHashSet.Contains(fileInfo.Name))
                {
                    filesHashSet.Add(fileInfo.Name);
                }
            }
        }
    }