{"raw_statement":[{"iden":"problem statement","content":"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.\nYou can do the following two kinds of operations any number of times in any order:\n\n*   Choose two stones (not necessarily adjacent) and swap them.\n*   Choose one stone and change its color (from red to white and vice versa).\n\nAccording 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?"},{"iden":"constraints","content":"*   $2 \\leq N \\leq 200000$\n*   $c_i$ is `R` or `W`."},{"iden":"input","content":"Input is given from Standard Input in the following format:\n\n$N$\n$c_{1}c_{2}...c_{N}$"},{"iden":"sample input 1","content":"4\nWWRR"},{"iden":"sample output 1","content":"2\n\nFor example, the two operations below will achieve the objective.\n\n*   Swap the $1$\\-st and $3$\\-rd stones from the left, resulting in `RWWR`.\n*   Change the color of the $4$\\-th stone from the left, resulting in `RWWW`."},{"iden":"sample input 2","content":"2\nRR"},{"iden":"sample output 2","content":"0\n\nIt can be the case that no operation is needed."},{"iden":"sample input 3","content":"8\nWRWWRWRR"},{"iden":"sample output 3","content":"3"}],"translated_statement":null,"sample_group":[],"show_order":["default"],"formal_statement":null,"simple_statement":null,"has_page_source":true}