#include<bits/stdc++.h>
int main() {
std::cin.tie(nullptr)->sync_with_stdio(false);
int n;
std::cin >> n;
std::string s;
std::cin >> s;
std::vector<int> wh, bl;
for (int i = 0; i < s.size(); ++i) {
if (s[i] == 'W') wh.push_back(i);
else bl.push_back(i);
}
long long ans = 0;
for (int k = 0; k < n; ++k, std::rotate(bl.begin(), bl.begin() + 1, bl.end())) {
long long cur = 0;
for (int i = 0; i < n; ++i) {
cur += std::min(2 * n - std::abs(bl[i] - wh[i]), std::abs(bl[i] - wh[i])) - 1;
}
ans = std::max(ans, cur);
}
std::cout << ans / 2;
}
