#include <cstdio>
#include <algorithm>

using namespace std;

struct chara {
    char x;
    int y;
};

bool smen(chara a,chara b){
    if ( a.x<b.x )return 1;
    if ( a.y<b.y )return 1;
    return 0;
}

char c,fin[10001];

int vf[27],t,n;

int main()
{
    FILE*f=fopen("litere.in","r");
    FILE*h=fopen("litere.out","w");
    fscanf(f,"%d%c",&n,&c);
    for ( int i=1;i<=n;++i ){
        fscanf(f,"%c",&fin[i]);
        fin[i]-='a'+1;
        vf[fin[i]]++;
        for ( int j=fin[i]+1;j<=26;++j )
            t+=vf[j];
    }
    fprintf(h,"%d",t);
    return 0;
}