#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int C(char a, char b) {
return a == b ? a == 'B' ? -1 : 1 : 0;
}
int main() {
cin.tie(nullptr)->sync_with_stdio(false);
int n;
string s;
cin >> n >> s;
vector<int> cnt(2 * n);
vector<int> v;
for (int i = 0, curr = n; i < n; i++) {
curr += C(s[i], s[n + i]);
cnt[curr]++;
v.push_back(curr);
}
int median = -1;
for (int i = 0, k = 0; k <= n / 2; i++) {
if (k + cnt[i] > n / 2)
median = i;
k += cnt[i];
}
ll ans = ll(n) * ll(n - 1) / 2ll;
for (int x : v)
ans -= abs(x - median);
cout << ans;
}
