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

end = 10 ** 15
start = 0

def calc(mid):
    n = 0
    now = 0
    for i in range(N):
        a = A[i]
        if a + now < mid:
            u = (mid - a - now + i) // (i + 1)
            n += u
            now += u * (i + 1)
            if n > K:return False
    return True
            

while end - start > 1:
    mid = end + start >> 1
    if not calc(mid):
        end = mid
    else:
        start = mid
print(start)