def main():
    N, K = map(int, input().split())
    S = input()

    if K < 2:
        print(S)
        return

    s = list(S)
    flag = [None] * N
    for i in range(N - 1):
        for j in range(97, 123):
            try:
                idx = s[i:].index(chr(j)) + i
                if idx == i:
                    break
            except:
                idx = -1

            if idx > -1:
                s[i], s[idx] = s[idx], s[i]
                flag[i] = flag[idx] = 1
                break

        if flag.count(1) == K:
            break

    print(*s, sep='')

main()