#include <bits/stdc++.h>     //   All praise is due to Allah alone, and peace and blessings be
using namespace std;         //         upon him, after whom there is no other Prophet.

int32_t main() {
    cin.tie(0)->sync_with_stdio(false);

    int32_t Case = 1;    //cin >> Case;
    for (int T = 1; T <= Case; T++) {

        int n, k; cin >> n >> k;
        string s; cin >> s;

        function<void()> Test_Case = [&]() {
            for(int i = 0; i < n; i += k) {
                sort(s.begin() + i, s.begin() + min(n, i + k));
            }
            cout << s << '\n';
        };
        Test_Case();
    }
    return 0;
}