#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)

using namespace std;

int main() {
    int n; string s;
    cin >> n >> s;
    
    int C = 0;
    for (char c : s) {
        if (c != 'A') C++;
    }
    
    int ans = 0, A = 0;
    for (char c : s) {
        if (c != 'A') C--;
        if (c != 'C') A++;
        ans += min(A, C);
    }
    
    cout << ans << '\n';
    
    return 0;
}