#include <bits/stdc++.h>

using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
int n,t;
char ch[10001];
int main()
{
    fin>>n;
    for(int i1=0;i1<n;i1++)
    {
        fin>>ch[i1];
        for(int i2=i1-1;i2>=0;i2--)
            if (ch[i1]<ch[i2])t++;
    }
    fout<<t<<'\n';
}