class Solver:
    def __init__(self, data, num):
        self.data = data
        self.num = int(num) - 1
        self.data_length = len(data)

    def decode_BWT(self):
        counter = {}
        transform = []
        for ch in self.data:
            counter[ch] = 0
            transform.append(0)
        for ch in self.data:
            counter[ch] += 1

        sum = 0
        k_list = list(counter.keys())
        k_list.sort()
        for ch in k_list:
            sum = sum + counter[ch]
            counter[ch] = sum - counter[ch]

        for i in range(0, self.data_length):
            transform[counter[self.data[i]]] = i
            counter[self.data[i]] += 1

        j = transform[self.num]
        ans = ''
        for i in range(0, self.data_length):
            ans += self.data[j]
            j = transform[j]

        return ans


if __name__ == '__main__':
    n = input()
    d = input()
    s = Solver(d, n)
    ans = s.decode_BWT()
    print(ans)