#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;

typedef unsigned long long LL;

const int maxn=1e5+100;

char buf[40],s[maxn];
LL ans,numo,l,c[maxn],numw[maxn];

template<class T> inline bool getd(T& x)
{
	int ch=getchar();
	bool neg=false;
	while(ch!=EOF && ch!='-' && !isdigit(ch)) ch=getchar();
	if(ch==EOF) return false;
	if(ch=='-'){
		ch=getchar();
		neg=true;
	}
	x=ch-'0';
	while(isdigit(ch=getchar())) x=x*10+ch-'0';
	if(neg) x=-x;
	return true;
}

template<class M> inline void putd(M x)
{
	int p=0;
	if(x<0){
		putchar('-');
		x=-x;
	}
	if(x==0) buf[p++]=0;
	while(x){
		buf[p++]=x%10;
		x/=10;
	}
	for(int i=p-1;i>=0;i--) putchar(buf[i]+'0');
	putchar('\n');
}

void init()
{
	getd(l);
	scanf("%s",s);
	memset(c,0,sizeof(c));
	memset(numw,0,sizeof(numw));
	for(int i=l-1;i>=0;i--){
		numw[i]=numw[i+1];
		if(s[i]=='W') numw[i]++; //numw[i]表示点i及其之后的w数量 
	}
	for(int i=0;i<l;i++){
		if(s[i]=='O') c[i]=numw[i];  
		if(i) c[i]+=c[i-1]; //维护其前缀和 
	}
}

void work()
{
	ans=0;
	for(int i=0;i<l;i++)
		if(s[i]=='C') ans+=c[l-1]-c[i];
	putd(ans);
}

int main()
{
	freopen("cowa.in","r",stdin);
	freopen("cowa.out","w",stdout);
	init();
	work();
	fclose(stdin);
	fclose(stdout);
	return 0;
}