#include <bits/stdc++.h>
using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");

int main()
{
    int N, cnt = 0;
    bool ordonat =  false;
    fin>>N;

    char s[N+2], copie[N+2];
    fin>>s;

    strcpy(copie, s);
    sort(copie, copie + sizeof(copie) - 1);

    while(strcmp(s, copie) != 0)
    {
        for(int i = 0; i<N-1; i++)
        {
            if(s[i] > s[i+1])
            {
                swap(s[i], s[i+1]);
                cnt++;
            }
        }
    }

    fout<<cnt;
}