How can I filter a dictionary using LINQ and return it to a dictionary from the same type

I have the following dictionary:

Dictionary<int,string> dic = new Dictionary<int,string>();
dic[1] = "A";
dic[2] = "B";

I want to filter the dictionary's items and reassign the result to the same variable:

dic = dic.Where (p => p.Key == 1);

How can I return the result as a dictionary from the same type [<int,string>] ?

I tried ToDictionary, but it doesn't work.