#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 2e5;
int countB[MAX_N + 1], countW[MAX_N + 1];
int main() {
int n;
string s;
cin >> n;
n *= 2;
cin >> s;
for (int i = n - 1; i >= 0; i--) {
countB[i] = countB[i + 1] + (s[i] == 'B');
countW[i] = countW[i + 1] + (s[i] == 'W');
}
int freeB = 0, freeW = 0;
queue<int> bs, ws;
vector<pair<int, int>> pairs;
for (int i = 0; i < n; i++) {
freeB += (s[i] == 'B');
freeW += (s[i] == 'W');
if (freeB > countW[i + 1] || freeW > countB[i + 1]) {
freeB -= (s[i] == 'B');
freeW -= (s[i] == 'W');
if (s[i] == 'B') {
pairs.push_back({ws.front(), i});
ws.pop();
} else {
pairs.push_back({bs.front(), i});
bs.pop();
}
} else {
if (s[i] == 'B')
bs.push(i);
else
ws.push(i);
}
}
int inter = 0;
for (auto x: pairs) {
for (auto y: pairs) {
if (x.second >= y.second)
continue;
if (x.second > y.first && x.first < y.first)
inter++;
}
}
cout << inter << "\n";
}
