#include <iostream>
#include <string>

using namespace std;

#define MAXN 10000

char s[MAXN + 1];

int main()
{
    FILE *fin, *fout;
    fin = fopen("litere.in", "r");
    fout = fopen("litere.out", "w");
    int N, i, j, ras = 0;
    fscanf(fin, "%d", &N);
    fgetc(fin);
    for (i = 0; i < N; i++){
        s[i] = fgetc(fin);
    }
    for (i = 0; i < N; i++){
        for (j = 0; j < i; j++){
            if (s[i] < s[j]){
                ras++;
            }
        }
    }
    fprintf(fout, "%d", ras);
    fclose(fin);
    fclose(fout);
    return 0;
}