#include <bits/stdc++.h>
using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
int a[10003], b[10003], n, cnt;

void Intercl(int st, int m, int dr)
{
    int i, j, k;
    k = i = st;
    j = m + 1;
    while (i <= m && j <= dr)
        if (a[i] <= a[j]) b[k++] = a[i++];
        else
        {
            b[k++] = a[j++];
            cnt += m - i + 1;
        }
    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 Msort(int st, int dr)
{
    if (dr - st >= 1)
    {
        int m = (st + dr) / 2;
        Msort(st, m);
        Msort(m + 1, dr);
        Intercl(st, m, dr);
    }
}
int main()
{
    int i;
    char x;
    fin >> n;
    for (i = 1; i <= n; i++)
    {
        fin >> x;
        a[i] = x;
    }
    Msort(1,n);
    fout << cnt;
    return 0;
}