#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <ctime>
#include <cstdlib>
#include <cstdio>
#include <fstream>

using namespace std;

string zad1(int N, int K, string text) {
	int i = N - 2;

	sort(text.begin(), text.end());

	while (i >= 0 && text.length() > K) {
		if (text[i] == text[i + 1]) {
			text = text.substr(0, i) + text.substr(i + 1, text.length());
		}

		i--;
	}

	return text;
}

int main() {
	int N, K;
	string text;
	fstream myFile;
	myFile.open("letters.in");

	myFile >> N >> K;
	myFile.close();

	myFile.open("letters.out");
	myFile << zad1(N, K, text);
	myFile.close();

	return 0;
}