#include <iostream>
#include <vector>
#include <string>
#include <functional>
#include <cassert>
using namespace std;
typedef long long ll;
const int N = 400000 + 7;
int n;
string s;
int main() {
ios::sync_with_stdio(0); cin.tie(0);
cin >> n >> s;
function<ll(vector<int>, vector<int>)> compute = [&](vector<int> a, vector<int> b) {
ll sol = 0;
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
if (min(a[i], b[i]) < min(a[j], b[j]) && min(a[j], b[j]) < max(a[i], b[i]) && max(a[i], b[i]) < max(a[j], b[j])) {
sol++;
}
}
}
return sol;
};
function<vector<int>(vector<int>, int)> shift = [&](vector<int> a, int cnt) {
vector<int> b((int)a.size());
for (int i = 0; i < (int)a.size(); i++) {
b[(i + cnt) % (int)a.size()] = a[i];
}
return b;
};
vector<int> a, b;
for (int i = 0; i < 2 * n; i++) {
if (s[i] != s[0]) {
a.push_back(i);
}
else {
b.push_back(i);
}
}
ll sol = 0;
for (int cnt = 0; cnt < n; cnt++) {
sol = max(sol, compute(a, shift(b, cnt)));
}
cout << sol << "\n";
}
