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

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

int main(void) {
    int n, cnt = 0;
    char s[10001];
    
    fin >> n;
    fin >> s;
        
    for(int i = 0; i < n - 1; i++)
        for (int j = i + 1; j < n; j++)
            if (s[i] > s[j])
                cnt++;
                
    fout << cnt;
    
    return 0;
}