#include <fstream>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <climits>

#include <ctype.h>


using namespace std;

//ifstream f("in.in");
//ofstream g("out.out");

ifstream f("litere.in");
ofstream g("litere.out");

char x;
int v[256],n;
long long sol=0;

int main(){

    f>>n;
    for(int i=1;i<=n;i++){
        f>>x;
        v[x]++;
        for(int j=x+1;j<='z';j++){
            sol+=v[j];
        }
    }
    g<<sol;

    f.close();
    g.close();
    return 0;
}