#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pil = pair<int, ll>;
using pli = pair<ll, int>;
using pll = pair<ll, ll>;
using vint = vector<int>;
using vll = vector<ll>;
using vld = vector<ld>;
using vpii = vector<pii>;
using vpil = vector<pil>;
using vpli = vector<pli>;
using vpll = vector<pll>;
#define x first
#define y second
#define all(v) v.begin(),v.end()
namespace BIT {
int n;
vint d;
void i(int n_) { n = n_; d = vint(n + 1); }
void u(int x, int v){ for(x++; x <= n; x += x & -x) d[x] += v; }
int g(int x){ int r = 0; for(x++; x; x &= x - 1) r += d[x]; return r; }
int g(int s, int e) { return g(e) - g(s - 1); }
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n;
string s;
cin >> n >> s;
vint w, b;
for(int i = 0; i < 2 * n; i++) (s[i] == 'W' ? w : b).push_back(i);
ll ans = 0;
vll memo(n, -1LL);
auto f = [&](int t) {
if(memo[t] >= 0) return memo[t];
vint mat(2 * n);
for(int i = 0; i < n; i++) {
int A = w[i], B = b[(i + t) % n];
mat[A] = B;
mat[B] = A;
}
BIT::i(2 * n);
ll cur = 0;
for(int i = 0; i < 2 * n; i++) {
if(i < mat[i]) BIT::u(i, 1);
else {
cur += BIT::g(mat[i] + 1, i - 1);
BIT::u(mat[i], -1);
}
}
ans = max(ans, cur);
return memo[t] = cur;
};
if(n <= 4000) {
for(int i = 0; i < n; i++) f(i);
cout << ans << '\n';
}
else {
int st = (f(0) < f(1));
int en = (f(n - 2) < f(n - 1));
if(st != en) {
int l = 0, r = n - 2;
while(l < r) {
int m = (l + r + 1) / 2;
if(f(m) < f(m + 1)) l = m;
else r = m - 1;
}
}
else if(st == 0) {
int l = 0, r = n - 2;
for(; ; l += (n / 20)) if(f(l) < f(l + 1)) break;
while(l < r) {
int m = (l + r + 1) / 2;
if(f(m) < f(m + 1)) l = m;
else r = m - 1;
}
}
else{
int l = 0, r = n - 2;
for(; ; r -= (n / 20)) if(f(r) >= f(r + 1)) break;
while(l < r) {
int m = (l + r + 1) / 2;
if(f(m) < f(m + 1)) l = m;
else r = m - 1;
}
}
cout << ans << '\n';
}
return 0;
}
