#include <cstdio>

using namespace std;
char v[10001];
char lit[30];
int main()
{
    FILE *in,*out;
    in=fopen("litere.in","r");
    out=fopen("litere.out","w");
    int n,i,j,ci;
    long long cate,acum,sum;
    char c;
    fscanf(in,"%d",&n);
    for(i=0;i<=n;i++)
    {
        v[i]=fgetc(in);
        lit[v[i]-96]++;
    }
    sum=0;
    ci=1;
    for(i=1;i<=29;i++)
    {
        if(lit[i]!=0)
        {
            cate=0;
            acum=0;
            for(j=1;j<=n;j++)
            {
                if(v[j]==i+96)
                {
                    acum=j-ci;
                    if(acum<0)
                        acum=0;
                    sum=sum+acum;
                    cate++;
                    ci++;
                }
            }
        }
    }
    fprintf(out,"%lld",sum);
    return 0;
}