from sys import stdin
input=lambda :stdin.readline()[:-1]

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

def calc(mid):
  c=0
  num=0
  for i in range(n):
    if a[i]+num<mid:
      use=(mid-a[i]-num+i)//(i+1)
      c+=use
      num+=(i+1)*use
  return c<=k


ng,ok=10**15,-1
while abs(ng-ok)>1:
  mid=(ng+ok)//2
  if calc(mid):
    ok=mid
  else:
    ng=mid

print(ok)