......

#include<bits/stdc++.h>
#include<utility>
using namespace std;
int main()
{
	long long c=0,o=0,w=0;
	int n;
	string s;
	cin>>n;
	cin>>s;
	for(auto i:s)
	{
		if(i=='C') c++;
		else if(i=='O') o+=c;
		else w+=o;
	}
	cout<<w;
}