# [C# (.NET Core)], <s>186</s> 185 bytes

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

    using System;class P{static void Main(){var i=int.Parse(Console.ReadLine());Console.Write((i==0|i==60)?$"1900-{i%59+1}-{i%31}":DateTime.FromOADate(i+(i<60?1:0)).ToString("yyyy-M-d"));}}

[Try it online!][TIO-jqerfori]

[C# (.NET Core)]: https://www.microsoft.com/net/core/platform
[TIO-jqerfori]: https://tio.run/##NY5RC4IwHMS/ypCCDZlMIkFNJIqekiSFnof@iT/oBtsSxPzspg/dw3G/e7lrLG@0gWX5WFRvUo3WQZ82nbSWlJN10mFDBo0tKSQqyqZBGoIZKheU0ligF62s7iB4gmzvqIAylv67l0EHlGKWie9qkWD5zgtjIfiE@2Psh/MWDuHsJVfpoMYegpvR/eO8IUWf4ikSeZgIxoJaV86sH6k3ruIFb711ap6XJRI/ "C# (.NET Core) – Try It Online"

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-1 byte by replacing OR operator(||) with binary OR operator(|).