# [C# (Visual C# Interactive Compiler)], 145 bytes

<!-- language-all: lang-cs -->

    s=>{var t="";for(;t=="";){for(int i=0,l=1;i<l;i++)if(i==(l=s.Length)-1||s[i]!=s[i+1])t+=s[i];else t+=(s[i++]-48)*2;if(s!=t){s=t;t="";}}return t;}

[Try it online!][TIO-jqg87h55]

[C# (Visual C# Interactive Compiler)]: http://www.mono-project.com/docs/about-mono/releases/5.0.0/#csc
[TIO-jqg87h55]: https://tio.run/##bVE9b8MgEN39Ky5WB6hxZYgT4RIydsrewfIQWThBsmhlSFvJ4be7kA9VTXID3Hv33p1019q8tXp6O5h2Zd2gzY6cvzV0ICcr1@PXdgAn01R0HwMSTsYUjxFo40DLgvSSCr3qhc4yrDukpUS9tC8bZXZuj3N6PNpaNzMZ3ow22GUxa4TqrYIAUOSzJi85fmYiNLAz6fBopROnud4Pyh0GA074SSRJGFs3dQNOWWdBglHfcOXG5A/CyBgjUDJP/rF0OZ8H@oYtS84JcLq8VS8WtCLAClrdVqoqWti9p4pBgHLK70xXF30wqghBg6@gjxpeOlIeij7sIZxAbds9Oh0o7CKIzzvBCcD7oJ3aaKPQU6rNK4yxUheNJ6B@Pq@YRrxtXcAduiiyNMU@xWL6BQ "C# (Visual C# Interactive Compiler) – Try It Online"