#include <bits/stdc++.h>
using namespace std;
template<typename T>
void out(T x) { cout << x << endl; exit(0); }
#define watch(x) cout << (#x) << " is " << (x) << endl
using ll = long long;
const ll mod = 1e9+7;
const int maxn = 1e6 + 5;
int n;
string s;
bool used[maxn];
template<typename T> struct bit1 {
T add(T x, T y) {
return x+y;
}
int n;
vector<T> t;
void init(int n) {
this->n=n;
t.resize(n+10);
}
T qry(int i) {
T res=0;
for (; i>0; i-=i&-i) res=add(res,t[i]);
return res;
}
void upd(int i, T dx) {
assert(i>=1 && i<=n);
for (; i<=n; i+=i&-i) t[i]=add(t[i],dx);
}
};
bool isect(pair<int,int> p, pair<int,int> q) {
if (max(p.first,q.first) >= min(p.second,q.second)) return false;
if (p.first>q.first) swap(p,q);
if (p.first<=q.first && q.second<=p.second) return false;
return true;
}
ll eval_brute(vector<pair<int,int>> v) {
assert(int(v.size())==n/2);
for (auto &p: v) {
if (p.first>p.second) {
swap(p.first,p.second);
}
}
ll res = 0;
for (int i=0; i<n/2; i++) {
for (int j=i+1; j<n/2; j++) {
if (isect(v[i],v[j])) res++;
}
}
return res;
}
ll eval(vector<pair<int,int>> v) {
assert(int(v.size())==n/2);
int N = 0;
vector<pair<int,int>> ev;
map<int,int> close, open;
for (auto &p: v) {
if (p.first>p.second) {
swap(p.first,p.second);
}
p.first++;
p.second++;
N = max(N, p.second);
ev.push_back({p.first,0});
ev.push_back({p.second,1});
close[p.first]=p.second;
open[p.second]=p.first;
}
ll res = 0;
bit1<ll> bit;
bit.init(N);
sort(ev.begin(), ev.end());
for (auto p: ev) {
if (p.second==0) {
bit.upd(p.first,+1);
}
if (p.second==1) {
bit.upd(open[p.first],-1);
int l = open[p.first];
int r = p.first;
assert(l<=r);
res += (bit.qry(r)-bit.qry(l-1));
}
}
return res;
}
ll brute() {
ll best=0;
vector<int> B, W;
for (int i=0; i<n; i++) {
if (s[i]=='B') B.push_back(i); else W.push_back(i);
}
for (int iter=0; iter<n/2; iter++) {
vector<pair<int,int>> v;
for (int i=0; i<n/2; i++) {
v.push_back({B[i],W[i]});
}
ll res = eval(v);
//cout<<iter<<": "<<eval_brute(v)<<" "<<res<<endl;
best = max(best, res);
std::rotate(W.begin(), W.begin()+1, W.end());
}
return best;
}
int main() {
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
cin>>n>>s;
n *= 2;
cout<<brute()<<endl;
return 0;
}
