#include <iostream>
#include<cstring>
#include <fstream>
using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
int main()
{ char s[10000];
int n,p=0;
fin>>n;
fin.get();
fin.get(s,n+1);
for(int i=0;i<n-1;i++){
    for(int j=i+1;j<n;j++){
        if(s[i]>s[j]){
            p++;
        }
    }
}

fout<<p;

    return 0;
}