#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;

string maxSubsequence(string num, int k) {
    int n = num.size();
    // We need to remove (n - k) digits.
    int removals = n - k;
    string result;

    for (char digit : num) {
        // While we can remove more digits and the last digit in the result is less than the current digit,
        // remove the last digit.
        while (!result.empty() && removals > 0 && result.back() < digit) {
            result.pop_back();
            removals--;
        }
        result.push_back(digit);
    }

    // If we still have removals left, remove them from the end.
    while (removals > 0) {
        result.pop_back();
        removals--;
    }

    // The result might be longer than k if we never removed enough digits.
    return result.substr(0, k);
}

int main() {
    // Example: using digits from the array [4, 9, 0, 2] represented as string "4902"
    string num = "4902";
    int k = 2;
    cout << "Maximum subsequence of length " << k << ": " << maxSubsequence(num, k) << endl;
    return 0;
}