#include<cstdio>
#include<iostream>
#include<string>
using namespace std;
typedef long long LL;
int n;
LL ans,w[100000]={0},c[100000]={0};
string a;
int main()
{
	freopen("cowa.in","r",stdin);
	freopen("cowa.out","w",stdout);
	cin>>n;
	cin>>a;
	LL b=0;
	for(int i=0;i<n;i++)
	{
		if(a[i]=='C')
			b++;
		if(a[i]=='O')
		c[i]=b;
	}
	b=0;
	for(int i=n-1;i>=0;i--)
	{
		if(a[i]=='W')
			b++;
		if(a[i]=='O')
		   w[i]=b;
	}
	for(int i=0;i<n;i++)
	{
		ans+=c[i]*w[i];
		//cout<<c[i]<<" "<<w[i]<<endl;
	}
		
	cout<<ans;
	return 0;
}