#include <fstream>

using namespace std;

int main () {
    ifstream cin ("litere.in");
    ofstream cout ("litere.out");
    int n, f[30] = {0}, x;
    cin >> n;
    char a[10001];
    for (int i = 1; i <= n; i++)
        cin >> a[i];
    long long inversiuni = 0;
    for (int i = 1; i <= n; i++) {
        int val = a[i] - 'a';
        
        for (int j = val + 1; j < 26; j++) {
            inversiuni = inversiuni + f[j];
        }
        
        f[val]++; 
    }
    cout << inversiuni;
    
    
    return 0;
}