def solve(n, k, s):
    u = s + s[::-1]
    t = min(u[i:i + n] for i in range(n + 1))
    i, h = 0, t[0]
    for i, c in enumerate(t):
        if c != h:
            break
    j = i
    for _ in range(k - 1):
        j <<= 1
        if j >= n:
            return h * n
    return h * j + t[i:i + n - j]


n, k = map(int, input().split())
s = input()
print(solve(n, k, s))
