#include<fstream>
#include<iostream>
using namespace std;
ifstream in("litere.in");
ofstream out("litere.out");
char v[10009];

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