#include<stdio.h>
int i,n,l,y[10001],z[10001][26];
char s[10001],c;
int main() {
    freopen("litere.in","r",stdin),freopen("litere.out","w",stdout),scanf("%d\n",&n);
    for(i=1;i<=n;i++)
        scanf("%c",&s[i]),z[i][s[i]-'a']=++y[s[i]-'a'];
    for(i=1;i<=n;i++)
    for(c='a';c<='z';c++)
    if(!z[i][c-'a'])
        z[i][c-'a']=z[i-1][c-'a'];
    for(i=1;i<=n;i++)
    for(c='a';c<s[i];c++)
        l+=z[n][c-'a']-z[i][c-'a'];
    printf("%d",l);
}