#include <bits/stdc++.h>

#define F first
#define S second
#define PB push_back
#define MP make_pair
#define REP(i,a,b) for (int i = a; i <= b; i++)
#define debug(i) cout << i << endl;
#define debugarr(a) for(auto i : a) cout << i << " ";

#define ll long long
#define vi vector<int>
#define vll vector<ll>
#define pi pair<int,int>
#define pll pair<ll, ll>
#define vpi vector<pi>

#define N 100010
#define LEFT(x) (x<<1)
#define RIGHT(x) ((x<<1)|1)

using namespace std;

int arr[N];
pi tree[N * 4];

pi query(int i, int l, int r, int x, int y) {
    if(l >= x && r <= y) return tree[i];
    else if(r < x || l > y) return MP(-1,-1);
    else {
        int mid = (l+r)>>1;
        pi res = MP(-1, -1);
        if(x <= mid)
            res = query(LEFT(i), l, mid, x, y);
        if(y > mid) {
            pi q = query(RIGHT(i), mid+1, r, x, y);
            if(q.F > res.F)
                res = q;
            else if(q.F == res.F && q.S < res.S)
                res = q;
        }
        return res;
    }
}

void build(int i, int l, int r) {
    if(l == r) tree[i] = MP(arr[l], l);
    else {
        int mid = (l+r)>>1;
        build(LEFT(i), l, mid);
        build(RIGHT(i), mid+1, r);

        if(tree[LEFT(i)].F > tree[RIGHT(i)].F)
            tree[i] = tree[LEFT(i)];
        else if(tree[LEFT(i)].F < tree[RIGHT(i)].F)
            tree[i] = tree[RIGHT(i)];
        else {
            if(tree[LEFT(i)].S < tree[RIGHT(i)].S)
                tree[i] = tree[LEFT(i)];
            else
                tree[i] = tree[RIGHT(i)];
        }
    }
}

int main() {
    ios_base::sync_with_stdio(false);

    int n, d;
    while(cin >> n >> d && n != 0) {
        memset(tree, 0, sizeof tree);
        int need = n - d;
        for(int i = 1; i <= n; i++) {
            char k;
            cin >> k;
            arr[i] = k - '0';
        }
        build(1, 1, n);

        int last_choose = -1;
        string ans = "";
        while(need--) {
            pi next = query(1, 1, n, last_choose+1, n - need);
            last_choose = next.S;
            ans += (char) next.F + '0';
        }
        cout << ans << endl;
    }
}