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:

* Choose two stones (not necessarily adjacent) and swap them.
* Choose one stone and change its color (from red to white and vice versa).



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?

Constraints

* 2 \leq N \leq 200000
* c_i is `R` or `W`.

Input

Input is given from Standard Input in the following format:


N
c_{1}c_{2}...c_{N}


Output

Print an integer representing the minimum number of operations needed.

Examples

Input

4
WWRR


Output

2


Input

2
RR


Output

0


Input

8
WRWWRWRR


Output

3
import java.util.Arrays;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {


		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();

		String s = sc.next();

		char[] chAry = new char[n];

		for (int i=0; i<n; i++){

			chAry[i] = s.charAt(i);

		}

		char[] chAryCopy = chAry.clone();

		Arrays.sort(chAryCopy);

		int cnt = 0;
		for (int i=0; i<n; i++){

			if (chAry[i] != chAryCopy[i]){
				cnt ++;
			}
		}
		System.out.println(cnt / 2);

	}


}