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

/**
infoarena.ro/problema/litere
*/
ifstream fin("litere.in");
ofstream fout("litere.out");
char a[10005], b[10005];
int nr, n;

void Interclasare(int st, int m, int dr)
{
    int i,j,k;
    i = k = st;
    j = m + 1;
    while(i <= m && j <= dr)
        if(a[i] > a[j])
        {
            b[k++] = a[j++];
            nr += (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);
        Interclasare(st,m,dr);
    }
}

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