#include <iostream>
#include <algorithm>
#include <vector>
#include <fstream>

using namespace std;

int main() {
	ifstream in;
	in.open("letters.in");
	int n, k, br = 1;
	in >> n >> k;
	char a;
	vector<char> arra;

	for (int i = 0; i < n; i++) {
		in >> a;
		arra.push_back(a);
	}
	in.close();

	sort(arra.begin(), arra.end());
	int cnt = n;
	ofstream out;
	out.open("letters.out");
	int i = n - 2;

	while (i >= 0 && arra.size() > k) {
		if (arra[i] == arra[i + 1]) {
			arra.erase(arra.begin() + i);
		}

		i--;
	}

	i = arra.size()-1;

	while (arra.size() > k) {
		arra.erase(arra.begin() + i);
		i--;
	}

	for (int i = 0; i < arra.size(); i++) {
		out << arra[i];
	}
	out.close();
	return 0;
}