#include <bits/stdc++.h>
using namespace std;
ifstream fin ("litere.in");
ofstream fout ("litere.out");

/**
*/

int n, cnt;
char a[100001], b[100001];

void Interclasare(int st, int dr, int mij)
{
    int i, j, k;
    k = i = st; j = mij + 1;
    while (i <= mij && j <= dr)
    {
        if (a[i] > a[j])
        {
            b[k++] = a[j++];
            cnt += mij - i + 1;
        }
        else
        {
            b[k++] = a[i++];
        }
    }
    while (i <= mij)
        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 mij = (st + dr) / 2;
        Mergesort(st, mij);
        Mergesort(mij + 1, dr);
        Interclasare(st, dr, mij);
    }
}

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