#include <bits/stdc++.h>
#define LL long long
#define PII pair<int, int>
#define PLL pair<LL, LL>
#define all_of(v) (v).begin(), (v).end()
#define sort_unique(c) (sort(c.begin(),c.end()), c.resize(distance(c.begin(),unique(c.begin(),c.end()))))
#define fi first
#define se second
const int MAXN = 200005;
//const LL INF = (LL) 1e9 + 8763;
//const LL MOD = (LL) 1e9 + 7;
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int n, arr[MAXN];
vector<int> W, B;
LL check2(int d) {
int res = 0;
for (int i = 0; i < n; i++) {
int mat1 = (i + d) % n;
for (int j = 0; j < i; j++) {
int mat2 = (j + d) % n;
int l1 = W[i], r1 = B[mat1];
int l2 = W[j], r2 = B[mat2];
if (l1 > r1) swap(l1, r1);
int in1 = (l1 <= l2 && l2 <= r1), in2 = (l1 <= r2 && r2 <= r1);
res += (in1 != in2);
}
}
return res;
}
void solve() {
cin >> n;
for (int i = 0; i < 2 * n; i++) {
char ch;
cin >> ch;
arr[i] = (ch == 'B');
if (arr[i]) B.push_back(i);
else W.push_back(i);
}
LL ans = 0;
// for (int d = 0; d < n; d++) {
// ans = max(ans, check(d));
// }
for (int d = 0; d < n; d++) {
ans = max(ans, check2(d));
}
cout << ans << '\n';
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0);
int tc = 1;
// cin >> tc;
for (int i = 1; i <= tc; i++) {
solve();
}
return 0;
}
