Burger Time?#784
Everybody knows that along major highways there are countless fast food restaurants—hamburgers, hot dogs, pizzas, sandwiches—so food can be found everywhere.
Often, the problem is not finding a restaurant but a drugstore. After a big lunch with fast food, it is normal to need a drugstore because your stomach might begin to hurt.
Given the locations of restaurants and drugstores on a highway, determine the minimum distance between a restaurant and a drugstore.
The first line of each test case contains an integer (1 \leq L \leq 2\,000\,000), the length of the highway.
The second line contains a string of length that shows the positions of restaurants and drugstores along the highway, as follows:
The character R represents a place with a restaurant.
The character D represents a place with a drugstore.
The character Z represents a place with both a restaurant and a drugstore.
The character . represents an empty place.
You may assume each test case has at least one restaurant and at least one drugstore.
The end of input is indicated when L = 0.
For each case in the input, print one line with the minimum distance between a restaurant and a drugstore.
Example 1