#include <bits/stdc++.h>
using namespace std;



char a[10002], b[10002];
int n,cnt;
ifstream fin("litere.in");
ofstream fout("litere.out");

void Intercl(int st, int m, int dr)
{
    int i, j, k;
    k = st;
    i = st; j = m+1;
    while (i <= m && j <= dr)
        if (a[i] > a[j]) b[k++] = a[j++], cnt += m-i+1;
        else b[k++] = a[i++];
    while (i <= m) b[k++] = a[i++];
    while (j <= dr) b[k++] = a[j++];

    for (i = st; i <= dr; i++)
        a[i] = b[i];
}

void MergeSort(int st, int dr)
{
    if (dr - st >= 1)
    {
        int m = (st + dr) / 2;
        MergeSort(st, m);
        MergeSort(m+1, dr);
        Intercl(st, m, dr);
    }
}

int main()
{
    int i;
    fin >> n;
    for (i = 0; i < n; i++)
        fin >> a[i];
    MergeSort(0, n-1);
    fout << cnt;
    return 0;
}