#include<iostream>
#include<cstdio>
#include<cstring>
#include<vector>
using namespace std;
class student
{
public:
	long long c,o,w;
	void init(){
		c=0;o=0;w=0;
	}
}sum;
int n;
long long ans=0;
vector<int>Count;
string str;
/*===============================================================*/
int main()
{
	freopen("cowa.in","r",stdin);
	freopen("cowa.out","w",stdout);
	cin>>n;
	cin>>str;
	for(int i=0;i<n;i++)
	{
		if(str[i]=='C')
			Count.push_back(sum.o);
		if(str[i]=='O')
		{
			sum.o++;
		}
		if(str[i]=='W')
		{
			for(int j=0;j<Count.size();j++)
			{
				ans+=(sum.o-Count[j]);
			}
		}
	}
	cout<<ans;
	return 0;
}