N,K=map(int, input().split())
A=list(map(int, input().split()))
ok,ng=0,10**15
while ng-ok>1:
  mid=(ok+ng)//2
  c=0
  base=0
  for j in range(N):
    a=base+A[j]
    if mid>a:
      cc=(mid-a-1)//(j+1)+1
      base+=cc*(j+1)
      c+=cc 
  if c>K:
    ng=mid 
  else:
    ok=mid 
print(ok)