#include <stdio.h>
#include <stdlib.h>
int v[10001],f[27];
int main()
{
    int n,i,perm,j;
    freopen("litere.in","r",stdin);
    freopen("litere.out","w",stdout);
    scanf("%d",&n);
    getchar();
    for(i=1; i<=n; i++)
        v[i]=getchar();
    for(i=1; i<=n; i++)
        v[i]=v[i]-'a'+1;
    perm=0;
    for(i=1; i<=n; i++)
    {
        for(j=v[i]+1; j<=26; j++)
            perm+=f[j];
        f[v[i]]++;
    }
    printf("%d\n",perm);


    return 0;
}