#include<fstream>
#include<algorithm>
#include<vector>
#include<cstring>
//#include<iostream>
using namespace std;
ifstream cin("litere.in");
ofstream cout("litere.out");
char s[10005];
int main() {
    int n,cnt=0;
cin>>n;
cin>>s;
n--;
for(int i=0;i<n;i++)
    for(int j=0;j<n;j++)
        if(s[j]>s[j+1])
        {
            swap(s[j],s[j+1]);
            cnt++;
        }
cout<<cnt;
}