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

int main(void) {
    ifstream fin("litere.in");
    ofstream fout("litere.out");
    char s[10001]; int n, cnt = 0;
    fin >> n >> s;
    
    for (int i = 1; i < n; i++)
        for (int j = 0; j < i; j++)
            if (s[j] > s[i])
                cnt++;
    
    fout << cnt;
    
    return 0;
}