/*
    Keep It Simple!
*/

#include <fstream>
#include <vector>
#include <list>
#include <stack>
#include <string>
#include <cmath>
#include <queue>
#include <vector>
#include <algorithm>

using namespace std;

ifstream fin("litere.in");
ofstream fout("litere.out");

#define ll long long
#define mp make_pair
#define fi first
#define se second
#define pb push_back

typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

const int kMaxN = 100100;
const int kMod = 9917;

ll bit[kMaxN];
int n,ans;
string aux;
pii v[kMaxN];

int read(int idx)
{
    int sum = 0;
    for(; idx; idx -= (idx&-idx))
        sum += bit[idx];
    return sum;
}

void update(int idx,int value)
{
    for(; idx<=n; idx += (idx&-idx))
        bit[idx] += value;
}

bool IdxComp(const pll &a, const pll &b)
{
    return a.se < b.se;
}

void Solve()
{
    fin >> n >> aux;
    for(int i=1;i<=n;++i)
        v[i].fi = aux[i-1],v[i].se=i;

    sort(v+1,v+n+1);

    for(int i=1; i<=n; ++i)
        v[i].fi = v[i-1].fi + 1;

    sort(v+1,v+n+1,IdxComp);

    for(int i=n;i;--i)
    {
        ans += read(v[i].fi);
        update(v[i].fi,1);
    }

    fout << ans << '\n';
    return;
}

int main()
{
    Solve();
    return 0;
}