#include <bits/stdc++.h>
using namespace std;

typedef long long i64;
typedef double db;
typedef vector<int> vi;
typedef pair<int, int> pii;

template<typename T>
inline T read() {
    T x = 0, f = 0;
    char ch = getchar();

    while (!isdigit(ch))
        f |= (ch == '-'), ch = getchar();

    while (isdigit(ch))
        x = x * 10 + (ch ^ 48), ch = getchar();

    return f ? -x : x;
}

#define rdi read<int>
#define rdi64 read<i64>
#define fi first
#define se second
#define pb push_back
#define mp make_pair

const int N = 4e5 + 10;

int n, c[N];
char s[N];

int main() {
#ifdef LOCAL
    freopen(".in", "r", stdin);
    freopen(".out", "w", stdout);
#endif
    n = rdi();
    scanf("%s", s + 1);

    for (int i = 1; i <= 2 * n; i++) {
        if (s[i] == 'B')
            c[i]++;
        else
            c[i <= n ? i + n : i - n]--;
    }

    for (int i = 1; i <= 2 * n; i++)
        c[i] += c[i - 1];

    sort(c + 1, c + 2 * n + 1);
    i64 ans = (i64)n * (n - 1);

    for (int i = 1; i <= n; i++)
        ans -= c[2 * n + 1 - i] - c[i];

    cout << (ans / 2) << endl;
    return 0;
}