#include <fstream>
using namespace std;
int f[30],v[10005];
int main()
{
    ifstream cin("litere.in");
    ofstream cout("litere.out");
    int cnt=0,n,sum=0;
    char ch;
    cin >> n;
    for(int i=0;i<n;i++)
    {
        cnt=0;
        cin >> ch;
        for(int j=ch+1;j<='z';j++)
        {
            cnt+=f[j-'a'];
        }
        f[ch-'a']++;
        sum=sum+cnt;
    }
    cout << sum;
    return 0;
}