#include <bits/stdc++.h>
#define NMAX 10005
using namespace std;

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

int main()
{
    int n, j = 1,cnt = 0;
    char v[NMAX], ch;
    in >> n >> v;
    for (int i = 0; i < n; ++i) {
        for (int j = 0;j < i; ++j)
            if(v[j] > v[i])
                cnt ++;
    }
    out << cnt;
    return 0;
}