#include <stdio.h>
#include <stdlib.h>
#define MAXC 26
#define MAXN 10000
int vf[MAXC],v[MAXN];
int main(){
    FILE*fi,*fout;
    int i,j,con,n;
    char a;
    fi=fopen("litere.in" ,"r");
    fout=fopen("litere.out" ,"w");
    fscanf(fi,"%d" ,&n);
    a=fgetc(fi);a=fgetc(fi);
    n=0;
    while(a>='a'&&a<='z'){
        v[n++]=a-'a';
        a=fgetc(fi);
    }
    con=0;
    for(i=0;i<n;i++){
        for(j=v[i]+1;j<MAXC;j++)
             con=con+vf[j];
        vf[v[i]]++;
    }
    fprintf(fout,"%d" ,con);
    fclose(fi);
    fclose(fout);
    return 0;
}