//https://www.infoarena.ro/problema/litere
#include <bits/stdc++.h>

using namespace std;

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

int main() {
    int n;
    in >> n;
    vector<char>a(n);
    for (auto &c : a)
        in >> c;

    bool ok = true;
    int cnt=0;
    while(ok){
        ok = false;
        for(int i=0;i<n-1;i++)
            if(a[i] > a[i+1]){
                swap(a[i],a[i+1]);
                ok=true;
                cnt++;
            }
    }
    // for(auto c:a)
    //     cout<<c<<' ';

    out<<cnt<<'\n';
    in.close(), out.close();
    return 0;
}