#include <bits/stdc++.h>
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);
///freopen ("input", "r", stdin);
cin >> n >> s;
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);
}
}
vector<ll> cnt(n);
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
if (a[i] < b[j]) {
cnt[(n - i + j) % n] += min(b[j] - a[i] - 1, 2 * (n - 1) - (b[j] - a[i] - 1));
}
}
for (int j = 0; j < n; j++) {
if (a[i] > b[j]) {
cnt[(n - i + j) % n] += min(a[i] - b[j] - 1, 2 * (n - 1) - (a[i] - b[j] - 1));
}
}
}
ll sol = 0;
for (auto& x : cnt) {
sol = max(sol, x);
}
cout << sol / 2 << "\n";
}
