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

def  cal(x):
    cnt = 0
    now = 0
    for i in range(n):
        if now + a[i] < x:
            t=now + a[i]
            v,m=divmod(x-t,i+1)
            if m>0:
                v+=1
            cnt += v
            now += v * (i+1)

    # print(cnt,x)
    if cnt <= k:
        return True
    else:
        return False

ok = 0
ng = 10 ** 15
while ng - ok > 1:

    mid = (ng+ok)//2
    if cal(mid):
        ok = mid
    else:
        ng = mid

print(ok)