#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);
    return 0;
}