C# Addition between objects that are numbers

I'm trying to find the best way to do following:

I have two Objects, object A and B. At some point in the program I know A and B are of type int, double or float. I would like to make an addition to them so A + B = C. C will be typed as we're used to while making addition between ints, floats, and doubles.

For example, if A was int and B float. Then C would be float.

The closest you can come is:

dynamic a = ...;
dynamic b = ...;
dynamic c = a + b;

That will perform the appropriate kind of addition, but you won't know the type of the result until execution time.

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