import sys
#sys.setrecursionlimit(500000)
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def TI(): return tuple(map(int,sys.stdin.readline().rstrip().split()))
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip())
#for i, pi in enumerate(p):
from collections import defaultdict,deque
import bisect
import itertools
dic = defaultdict(int)
d = deque()
YN = ['No','Yes']

N,K = MI()
A = LI()
#https://aotamasaki.hatenablog.com/entry/meguru_bisect
def is_ok(arg):
  count = 0
  plus = 0
  for i in range(1,N+1):
    ap = A[i-1]+plus
    if ap < arg:
      h = (arg-ap+i-1)//i
      count += h
      if count > K:
        return False
      plus += h*i
  if count <= K:
    return True
  else:
    return False
      
    

def meguru_bisect(ng, ok):
    '''
    初期値のng,okを受け取り,is_okを満たす最小(最大)のokを返す
    まずis_okを定義すべし
    ng ok は  とり得る最小の値-1 とり得る最大の値+1
    最大最小が逆の場合はよしなにひっくり返す
    '''
    while (abs(ok - ng) > 1):
        mid = (ok + ng) // 2
        if is_ok(mid):
            ok = mid
        else:
            ng = mid
    return ok
print(meguru_bisect(10**14+10**10,0))