N,K = map(int,input().split())
A = [-1] + list(map(int,input().split()))

OK = 0
NG = 10**30
while NG - OK >= 2:
    MID = (OK + NG) // 2
    count = 0
    now_plus = 0
    for i in range(1,N+1):
        if A[i] + now_plus < MID:
            k = -(-(MID - A[i] - now_plus) // i)
            count += k
            now_plus += i * k
    #print(MID,count)
    if count > K:
        NG = MID
    else:
        OK = MID
print(OK)