#include <fstream>
using namespace std;
ifstream in("date.in");
ofstream out("date.out");
int main() {

    int n;
    char c[10001];

    int cnt = 0;

    in >> n;

    for (int i = 0; i < n; i++) {
        in >> c[i];
    }

    for (int i = 1; i < n; i++) {
        for(int j = 0; j < i; j++)
            if(c[i] - '0' < c[j] - '0')
                cnt++;
    }

    out << cnt;

    return 0;
}