#include <fstream>

using namespace std;

ifstream cin("litere.in");
ofstream cout("litere.out");


int main(){
    int N, rez = 0;
    cin >> N;
    char v[100005];
    cin >> v;
    for (int i = 1; i < N; ++i)
        for (int j = 0; j < i; ++j)
            if ((int)v[j] > (int)v[i])
                ++rez;

    cout << rez;

    return 0;
}