n,k = map(int,input().split())
A = list(map(int,input().split()))


def calc(x):
    count = 0
    left = k
    for i,a in enumerate(A,1):
        na = a+count
        if na >= x:
            continue
        need = (x-na+i-1)//i
        if need > left:
            return False
        count += need*i
        left -= need

    return True



l = 0
r = 10**20
while r > l + 1:
    m = (r+l)//2
    if calc(m):
        l = m
    else:
        r = m
print(l)