Score : 400 points
An altar enshrines N stones arranged in a row from left to right. The color of the i-th stone from the left (1 \leq i \leq N) is given to you as a character c_i; R
stands for red and W
stands for white.
You can do the following two kinds of operations any number of times in any order:
According to a fortune-teller, a white stone placed to the immediate left of a red stone will bring a disaster. At least how many operations are needed to reach a situation without such a white stone?
R
or W
.Input is given from Standard Input in the following format:
N c_{1}c_{2}...c_{N}
Print an integer representing the minimum number of operations needed.
4 WWRR
2
For example, the two operations below will achieve the objective.
RWWR
.RWWW
.2 RR
0
It can be the case that no operation is needed.
8 WRWWRWRR
3