{"problem":{"name":"Alter Altar","description":{"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` st","description_type":"Markdown"},"platform":"AtCoder","limit":{"time_limit":2000,"memory_limit":262144},"difficulty":"None","is_remote":true,"is_sync":true,"sync_url":null,"sign":"abc174_d"},"statements":[{"statement_type":"Markdown","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?\n\n## Constraints\n\n*   $2 \\leq N \\leq 200000$\n*   $c_i$ is `R` or `W`.\n\n## Input\n\nInput is given from Standard Input in the following format:\n\n$N$\n$c_{1}c_{2}...c_{N}$\n\n[samples]","is_translate":false,"language":"English"}],"meta":{"iden":"abc174_d","tags":[],"sample_group":[["4\nWWRR","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`."],["2\nRR","0\n\nIt can be the case that no operation is needed."],["8\nWRWWRWRR","3"]],"created_at":"2026-03-03 11:01:14"}}