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
//I AM THE CREED
/* //I AM THE CREED
/* package codechef; // don't place package name! */
import java.io.BufferedReader; 
import java.io.IOException; 
import java.io.InputStreamReader; 
import java.util.StringTokenizer; 
import java.util.*;
public class Main{
    public static void main(String[] args) throws IOException 
    { 
  
        Scanner input = new Scanner(System.in);
        while(input.hasNext()){
          int n=input.nextInt();
          String s=input.next();
          
          int min=Integer.MAX_VALUE;
          int right=0;
          int left=0;
          for(int i=0;i<s.length();i++){
              if(s.charAt(i)=='R'){
                  left++;
              }
          }
          min=left;
          for(int i=s.length()-1;i>=0;i--){
              if(s.charAt(i)=='R'){
                 left--;
                 int moves=Math.max(right, i-left);
                 
                 min=Math.min(min, moves); 
                 right++;
              }
          }
          System.out.println(min);
        }
        
    }
    


}