#include <bits/stdc++.h>
using namespace std;
struct BIT
{
int n;
vector<int> bit;
BIT(int n_) : n(n_), bit(n + 1) {}
void add(int i, int u)
{
for (; i <= n; i += i & -i)
{
bit[i] += u;
}
}
int query(int i)
{
int ret = 0;
for (; i > 0; i -= i & -i)
{
ret += bit[i];
}
return ret;
}
int query(int l, int r)
{
return query(r) - query(l);
}
};
int main()
{
cin.tie(0)->sync_with_stdio(0);
int n;
cin >> n;
int N = 2 * n;
string a;
cin >> a;
vector<int> b, c;
for (int i = 0; i < N; i++)
{
if (a[i] == 'B')
{
b.push_back(i);
}
else
{
c.push_back(i);
}
}
auto solve = [&](int t) -> long long
{
vector<pair<int, int>> res;
for (int i = 0; i < t; i++)
{
res.emplace_back(min(b[i], c[n - t + i]), max(b[i], c[n - t + i]));
}
for (int i = t; i < n; i++)
{
res.emplace_back(min(b[i], c[i - t]), max(b[i], c[i - t]));
}
sort(res.begin(), res.end(), [&](pair<int, int> x, pair<int, int> y)
{
if (x.second != y.second)
{
return x.second < y.second;
}
return x.first < y.first;
});
long long ret = 0;
BIT bit(2 * n);
for (auto &[l, r] : res)
{
ret += bit.query(l, r);
bit.add(l + 1, -1);
bit.add(r + 1, 1);
}
return ret;
};
long long ans = 0;
for (int i = 0; i <= n; i++)
{
ans = max(ans, solve(i));
}
cout << ans << '\n';
return 0;
}
