Static readonly vs const in C#: what's the difference and which to choose?

Hi everyone! I'm a beginner C# developer and I'm confused about two similar concepts: `static readonly` and `const`. Both are used to declare immutable values, but I don't understand when to use each one.\n\nFor example, I'm writing a class for mathematical calculations:\n\n```csharp\npublic class MathHelper\n{\n public const double Pi = 3.14159;\n public static readonly double E = 2.71828;\n}\n```\n\nWhy not make both constants? Or both `static readonly`? What's the fundamental difference here?\n\nI've read that `const` works faster, but `static readonly` is somehow related to memory. I've also heard that `const` can only be used for primitive types, while `static readonly` can be used for any type. But I don't fully understand the practical implications.\n\nCan you explain with simple examples?