/**
 *    author: 小飞侠
 *    created: 2024.10.22 20:33:20
 */
#include <bits/stdc++.h>
using namespace std;
#define ls u << 1
#define rs u << 1 | 1
#define LL long long
#define int long long
#define PII pair <int, int>
#define fi first
#define se second
#define pub push_back
#define pob pop_back
#define puf push_front
#define pof pop_front
#define lb lower_bound
#define ub upper_bound
#define i128 __int128
#define pcnt(x) __builtin_popcount(x)
#define mem(a,goal) memset(a, (goal), sizeof(a))
#define rep(x,start,end) for(int x = (start) - ((start) > (end)); x != (end) - ((start) > (end)); ((start) < (end) ? x ++ : x --))
#define aLL(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
const int INF = 998244353;
const int P = 1e9 + 7;
const int N = 2e5 + 5;
int a[N];
int cnt[200][N];
int ans;
int n;

void solve()
{
    cin >> n;
    string s;
    cin >> s;
    for(int i = 0; i < n; ++ i) cnt[s[i] - 'a'][i] ++;

    for(int i = 0; i < 26; ++ i)
    {
        for(int j = 1; j < n; ++ j)
        {
            cnt[i][j] += cnt[i][j - 1];
        }
    }

    for(int i = 0; i < n; ++ i)
    {
        int t = s[i] - 'a';
        for(int j = 0; j < 26; ++ j)
        {
            if(j == t) continue;
            ans += (cnt[j][n - 1] - cnt[j][i]) * ((cnt[j][n - 1] - cnt[j][i]) - 1)/ 2;
        }
    }

    cout << ans << '\n';
}
signed main()
{
    solve();
    return 0;
}