#include<cstdio>
using namespace std;
int v[27];
char s[10001];
int main(){
    freopen ("litere.in","r",stdin);
    freopen ("litere.out","w",stdout);
    int n,i,j,k=0;
    scanf ("%d\n",&n);
    scanf ("%s",&s);
    for(i=0;i<n;i++){
        v[s[i]-'a']++;
        for(j=25;j>s[i]-'a';j--)
            k+=v[j];
    }
    printf ("%d",k);
    return 0;
}