https://codeforces.com/contest/462/problem/B

#include <iostream>
#include <map>
#include <algorithm>
#include <vector>

using namespace std;

int main()
{
    int n, k;
    cin >> n >> k;
    vector<unsigned long long> vec(300);
    for (int i = 0; i < n; i++) {
        char ch; cin >> ch;
        vec[ch]++;
    }
    sort(vec.begin(), vec.end(), [](auto a, auto b) {
        return a > b;
        });
    int count = 0;
    unsigned long long res = 0;
    for (auto i = 0; count < k; i++) {
        res += min(vec[i] * vec[i], 1ULL * (k - count) * (k - count));
        count += min(vec[i], 1ULL * (k - count));
    }
    cout << res << endl;
}