#include <bits/stdc++.h>
#define uwu return 0;
using namespace std;
#define fs first
#define sc second
const int SIZE = 2e5 + 5, MAGIC = 12;
string S;
int ps[2][SIZE];
int BITree[2 * 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;
}
long long eval(int x, int N){
for (int i = 0; i < 2 * N; i++){
BITree[i] = 0;
}
long long ans = 0;
vector <pair<int, int>> seg;
for (int i = 0; i < N; i++){
seg.push_back({ps[0][i], ps[1][(i + x) % N]});
seg.push_back({ps[1][(i + x) % N], ps[0][i]});
}
sort(seg.begin(), seg.end());
for (int i = 0; i < N; i++){
if(seg[i].sc > seg[i].fs){
ans += query(seg[i].sc);
modify(seg[i].sc, 1);
}
else{
modify(seg[i].fs, -1);
}
}
return ans;
}
int main(){
cin.tie(0), ios::sync_with_stdio(0);
int N;
cin >> N >> S;
int ptr[2] = {0, 0};
for (int i = 0; i < 2 * N; i++){
ps[S[i] == 'W'][ptr[S[i] == 'W']++] = i;
}
int L = 0, R = N - 1, M1, M2;
while (L != R){
M1 = L + (R - L) / 3;
M2 = R - (R - L) / 3;
if(eval(M1, N) < eval(M2, N))
L = M1 + 1;
else
R = M2 - 1;
}
cout << eval(L, N) << '\n';
uwu
}
