import sys

inputs = sys.stdin.readline

"""再帰関数のときセット
sys.setrecursionlimit(10**7)
import pypyjit
pypyjit.set_param('max_unroll_recursion=-1')
"""


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

    def judge(m):
        cnt = 0
        power = 0
        for i, a in enumerate(A):
            if cnt > K:
                break
            now_val = a + power
            if now_val < m:
                pl_cnt = (m - now_val) // (i + 1)
                if (m - now_val) % (i + 1):
                    pl_cnt += 1
                cnt += pl_cnt
                power += pl_cnt * (i + 1)
        return cnt <= K

    left, right = 0, 10 ** 15
    while right - left >= 2:
        mid = (left + right) // 2
        if judge(mid):
            left = mid
        else:
            right = mid - 1
    if judge(right):
        print(right)
    else:
        print(left)


if __name__ == '__main__':
    main()