## https://yukicoder.me/problems/no/2977


def solve2(N, K, A):
    array = []
    for i in range(N):
        for j in range(i + 1, N):
            array.append(A[i] ^ A[j])
    array.sort()
    print(array[K - 1])


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

    max_a = max(A)
    for k in reversed(range(40)):
        if (1 << k) & max_a > 0:
            max_k = k
            break
    A.sort()

    answer = 0
    target_ranges = [[i + 1, N - 1] for i in range(N)]
    target_ranges[N - 1] = [-1, -1]
    for k in reversed(range(max_k + 1)):
        array = [-1] * N
        for i in range(N):
            array[i] = 1 if (1 << k) & A[i] > 0 else 0
        
        # 0の数を計算
        z = 0        
        for i in range(N):
            if target_ranges[i][0] == -1:
                continue

            if array[i] == 0:
                if array[target_ranges[i][1]] == 0:
                    z += target_ranges[i][1] - target_ranges[i][0] + 1
                elif array[target_ranges[i][0]] == 0:
                    low = target_ranges[i][0]
                    high = target_ranges[i][1]
                    while high - low > 1:
                        mid = (high + low) // 2
                        if array[mid] == 0:
                            low = mid
                        else:
                            high = mid
                    if array[high] == 0:
                        z += high - target_ranges[i][0] + 1
                    else:
                        z += low - target_ranges[i][0] + 1
            else:
                if array[target_ranges[i][0]] == 1:
                    z += target_ranges[i][1] - target_ranges[i][0] + 1
                elif array[target_ranges[i][1]] == 1:
                    low = target_ranges[i][0]
                    high = target_ranges[i][1]
                    while high - low > 1:
                        mid = (high + low) // 2
                        if array[mid] == 1:
                            high = mid
                        else:
                            low = mid
                    if array[low] == 1:
                        z += target_ranges[i][1] - low + 1
                    else:
                        z += target_ranges[i][1] - high + 1

        if z < K:
            K -= z
            answer += (1 << k)
            for i in range(N):
                if target_ranges[i][0] == -1:
                    continue

                if array[i] == 0:
                    if array[target_ranges[i][1]] == 0:
                        target_ranges[i][0] = -1
                        target_ranges[i][1] = -1
                        continue
                    else:
                        # 1を求める
                        low = target_ranges[i][0]
                        high = target_ranges[i][1]
                        while high - low > 1:
                            mid = (high + low) // 2
                            if array[mid] == 1:
                                high = mid
                            else:
                                low = mid
                        if array[low] == 1:
                            target_ranges[i][0] = low
                        else:
                            target_ranges[i][0] = high
                else:
                    if array[target_ranges[i][0]] == 1:
                        target_ranges[i][0] = -1
                        target_ranges[i][1] = -1
                        continue
                    else:
                        # 0を求める
                        low = target_ranges[i][0]
                        high = target_ranges[i][1]
                        while high - low > 1:
                            mid = (high + low) // 2
                            if array[mid] == 0:
                                low = mid
                            else:
                                high = mid
                        if array[high] == 0:
                            target_ranges[i][1] = high
                        else:
                            target_ranges[i][1] = low
        else:
            # 0となる範囲を求める
            for i in range(N):
                if target_ranges[i][0] == -1:
                    continue

                if array[i] == 0:
                    if array[target_ranges[i][0]] == 1:
                        target_ranges[i][0] = -1
                        target_ranges[i][1] = -1
                        continue
                    else:
                        low = target_ranges[i][0]
                        high = target_ranges[i][1]
                        while high - low > 1:
                            mid = (high + low) // 2
                            if array[mid] == 0:
                                low = mid
                            else:
                                high = mid
                        if array[high] == 0:
                            target_ranges[i][1] = high
                        else:
                            target_ranges[i][1] = low
                else:
                    if array[target_ranges[i][1]] == 0:
                        target_ranges[i][0] = -1
                        target_ranges[i][1] = -1
                        continue
                    else:
                        low = target_ranges[i][0]
                        high = target_ranges[i][1]
                        while high - low > 1:
                            mid = (high + low) // 2
                            if array[mid] == 1:
                                high = mid
                            else:
                                low = mid
                        if array[low] == 1:
                            target_ranges[i][0] = low
                        else:
                            target_ranges[i][0] = high


    print(answer)




if __name__ == "__main__":
    main()