#include <bits/stdc++.h>

using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
char s[10002];
int n,cnt=0,ok;
int main()
{
    fin>>n;
    fin>>s;
    do
    {
        ok=1;
        for(int i=0;i<n-1;i++)
        {
            if(s[i]>s[i+1])
            {
                swap(s[i],s[i+1]);
                ok=0;
                cnt++;
            }
        }
    }while(ok==0);

    fout<<cnt;


    return 0;
}