The program must output the letter that is paired the most. For example, if your program was given the following string:

```
"Sally's friend Bobby searched for seashells."

```

it must output `L` because `"ll"` occurs twice, which is more frequent than the other pair `"bb"`.

Rules: 

* If more than one letter has 1st place for occurrences, then output all of them in alphabetical order (e.g. `"Sally's friends Jimmy and Bobby rummaged for seashells."` should output both `L` AND `M` [or `"LM"` if you please] because they both occur more frequently than other pairs.)
* Letters which are tripled, quadrupled, etc. count as one pair (e.g. `"lll"` in `"willless"` is counted as only one pair of `L`.)
* Letter pairs must be in one word (e.g. `"Sally's sociable friends Sammy and Bobby searched for fabulous seashells."` should output `L` and not `S` because despite `"ss"` having more occurrences than `"ll"`, they are separated by spaces.)
* Count only letters from the English alphabet
* Case does not matter (e.g. `"Ss"` is the same as `"SS"` or `"ss"`, and all are counted as one pair of `S`.)

You may read your input from wherever you please. Shortest code wins.