# [C# (.NET Core)], 186 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-jp2b7r5a]

[C# (.NET Core)]: https://www.microsoft.com/net/core/platform
[TIO-jp2b7r5a]: https://tio.run/##NY5RC4IwHMS/ypCCDZlMIiFNJIqekiSFnof@iT/oBtsSRP3spg/dw3G/e7mrLa@1gWX5WlQfUg7WQZfUrbSWFKN10mFNeo0NySUqysZeGoIpKhcU0ligV62sbiF4gWweqIAylvy7t0EHlGKaimlaPRIs23nhSQg@4v548sN5C4dw9uKbdFBhB8Hd6O552ZCiT/EciSyMBWNBpUtn1pPUG1bxnDfeujXPyxKJHw "C# (.NET Core) – Try It Online"