local n, k = io.read("*n", "*n")
k = 1LL * k
local a = {}
for i = 1, n do
  a[i] = 1LL * io.read("*n")
end

local function solve(x)
  local cnt = 0LL
  local sum = 0LL
  for i = 1, n do
    if sum + a[i] < x then
      local needadd = (x - sum - a[i] + i - 1LL) / (1LL * i)
      cnt = cnt + needadd
      if k < cnt then return false end
      sum = sum + needadd * i
    end
  end
  -- print(x, cnt)
  return true
end

local min, max = 0LL, 1LL * 1000000007 * 200000
while 1LL < max - min do
  local mid = (min + max) / 2LL
  if solve(mid) then
    min = mid
  else
    max = mid
  end
end
min = tostring(min):gsub("LL", "")
print(min)