Npgsql does not work with Visual studio 2013 C#

Question

I want to develop C# program with Visual studio 2013 based on database PostgreSQL

I downloaded Npgsql latest version 6.0 package from Nuget, it seems it does not work with VS2013. I cannot find the old version for Npgsql, which version is suitable for VS2013? Where can I get it?

Meanwhile, I don't know why. Integrated Manager Nuget packages in VS2013, it always keep searching packages, but cannot find anyone.