#include <cstdio>
#include <algorithm>

static const int N = (int)1e6;
static const int INF = (int)1e9;

int n, k;
char s[N + 2], t[N + 2];
int cnt[26], p[26];
int ans[26], ans_size;
int cur[26];

bool comp(const int &x, const int &y) {
    return cnt[x] < cnt[y];
}

int main() {
    freopen("input.txt", "rt", stdin);
    freopen("output.txt", "wt", stdout);

    scanf("%d%d\n%s", &n, &k, s);

    k = std::min(n, k);

    for (int i = 0; i < n; i++)
        cnt[s[i] - 'a']++;

    for (int i = 0; i < 26; i++)
        p[i] = i;

    std::sort(p, p + 26, comp);

    ans_size = INF;

    for (int i = 0, sum = 0; i < 26; i++) {
        if (sum > k)
            break;

        for (int j = i; j < 26; j++)
            cur[j] = cnt[p[j]];

        for (int j = 0; j < i; j++) {
            for (int k = 0; k < cnt[p[j]]; k++) {
                int p = i;

                for (int l = i; l < 26; l++)
                    if (cur[l] < cur[p])
                        p = l;

                cur[p]++;
            }
        }

        for (int j = sum; j < k; j++) {
            int pl = i, ph = i;

            for (int k = i; k < 26; k++) {
                if (cur[k] < cur[pl])
                    pl = k;
                if (cur[k] > cur[ph])
                    ph = k;
            }

            if (cur[pl] < cur[ph])
                cur[pl]++, cur[ph]--;
        }

        int pl = 0, ph = 0;

        for (int j = 0; j < 26; j++) {
            if (cur[j] > 0 && (cur[pl] == 0 || cur[j] < cur[pl]))
                pl = j;

            if (cur[j] > 0 && (cur[ph] == 0 || cur[j] > cur[ph]))
                ph = j;
        }

        if (cur[ph] - cur[pl] < ans_size)
        {
            ans_size = cur[ph] - cur[pl];

            for (int j = 0; j < 26; j++)
                ans[p[j]] = cur[j];
        }

        sum += cnt[p[i]], cur[i] = 0;
    }

    for (int i = 0; i < 26; i++) {
        for (int j = 0; j < n && ans[i] > 0; j++)
            if (t[j] == 0 && s[j] == i + 'a')
                t[j] = i + 'a', ans[i]--;
    }

    for (int i = 0; i < 26; i++) {
        for (int j = 0; j < n && ans[i] > 0; j++)
            if (t[j] == 0)
                t[j] = i + 'a', ans[i]--;
    }

    printf("%s", t);

    return 0;
}