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

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

int main() {
    
    int n;
    char s[10001];
    in >> n >> s;

    long long cnt = 0;
    for(int i = 1; i <= n; i++) {
        for(int j = 0; j < i; j++) {
            if(s[i] > s[j]) cnt++;
        }
    }
    out << cnt;
    return 0;
}