N, K = gets.split.map(&:to_i)
A = gets.split.map(&:to_i)

ok = 0
ng = A.max + K * N + 1

def f(x)
  k = K
  sum = 0

  A.each.with_index(1) do |a, i|
    a += sum

    if a < x
      diff = x - a
      op_cnt = (diff + i - 1) / i
      k -= op_cnt
      sum += i * op_cnt
    end

    if k < 0
      return false
    end
  end

  true
end

while (ok - ng).abs >= 2
  x = (ok + ng) / 2

  if f(x)
    ok = x
  else
    ng = x
  end
end

puts ok