C++ :

#include <bits/stdc++.h>

using namespace std;

using ll = long long;

const int S = 1 << 26;

ll n, res, dp;
ll f[S];
string s;

int main() {
    cin >> n >> s;
    
    for (int i = 0; i < n; i++) {
        dp ^= (1 << (s[i] - 'a'));
        if (dp == 0) res++;
        res += f[dp];
        f[dp]++;
    }

    cout << res << '\n';

    return 0;
}