#include <fstream>
#include <cstring>
using namespace std;
ifstream in("litere.in");
ofstream out("litere.out");

int cnt=0 ,sum=0 ,v[27] ,n;
char a[10000];

int main()
{
    in>>n>>ws;
    for(int i=0;i<n;i++)
    {
        in>>a[i];
        v[a[i]-'a'+1]++;
        cnt=0;
        for( int j=a[i]-'a'+2;j<=26;j++)
        {
            cnt+=v[j];
        }
        sum=sum+cnt;
    }
    out<<sum;
    return 0;
}