#include<bits/stdc++.h>

using namespace std;

int main()
{
	int k;
	cin>>k;

	string s;
	cin>>s;

	int countr=0;
	for(char c:s)
	{
		if(c=='R')
			countr++;
	}

	int ans=0;	
	for(int i=0;i<countr;i++)
	{
		if(s[i]=='R')
			ans++;
	}

	cout<<countr-ans;
	return 0;
}
### Prompt

Please formulate a CPP solution to the following problem:

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

### Response

```cpp
#include<bits/stdc++.h>

using namespace std;

int main()
{
	int k;
	cin>>k;

	string s;
	cin>>s;

	int countr=0;
	for(char c:s)
	{
		if(c=='R')
			countr++;
	}

	int ans=0;	
	for(int i=0;i<countr;i++)
	{
		if(s[i]=='R')
			ans++;
	}

	cout<<countr-ans;
	return 0;
}
```