Defining Local Variable const vs Class const

If I am using a constant that is needed only in a method, is it best to declare the const within the method scope, or in the class scope? Is there better performance declaring it in the method? If that is true, I think it's more standard to define them at class scope (top of file) to change the value and recompile easier.

public class Bob
{
   private const int SomeConst = 100; // declare it here?
   public void MyMethod()
   {
      const int SomeConst = 100; // or declare it here?
      // Do something with SomeConst
   }
}