#include <bits/stdc++.h>
#define uwu return 0;
using namespace std;
#define fs first
#define sc second
const int SIZE = 2e5 + 5;
string S;
deque <int> pos[2];
vector <pair<int, int>> seg;
int BITree[SIZE];
void modify(int pos, int val){
for (; pos < SIZE; pos += (pos & - pos)){
BITree[pos] += val;
}
return;
}
int query(int pos){
int ret = 0;
for (; pos; pos -= (pos & - pos)){
ret += BITree[pos];
}
return ret;
}
int main(){
cin.tie(0), ios::sync_with_stdio(0);
int N;
cin >> N >> S;
for (int i = N; i < S.size(); i++){
pos[S[i] == 'W'].push_back(i);
}
for (int i = 0; i < N; i++){
seg.push_back({i, pos[S[i] == 'B'].front()});
pos[S[i] == 'B'].pop_front();
}
long long ans = 0;
for (int i = 0; i < N; i++){
ans += query(seg[i].sc);
modify(seg[i].sc, 1);
}
cout << ans << '\n';
uwu
}
