#include <stack>
#include <iostream>
#include <algorithm>
using namespace std;

int main()
{
    stack<char> pilha;
    string s, res;
    int n, tot;
    while((cin >> n >> n) && n)
    {
        cin >> s;
        tot = 0;
        for(int i = 0; s[i] != '\0'; i++)
        {
             while(!pilha.empty() && s[i] > pilha.top() && tot < n)
                tot++, pilha.pop();
             pilha.push(s[i]);
        }
        while(tot < n)
        {
            pilha.pop();
            tot++;
        }
        res = "";
        while(!pilha.empty())
            res += pilha.top(), pilha.pop();
        reverse(res.begin(), res.end());
        cout << res << endl;
    }


}