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

table.sort(a)
local max_seg_size = 0
for i = 1, #a do
  local start = i
  local pos = start + 1
  local seg_size = 1
  while (pos <= #a) and (a[pos] - a[start] <= 1) do
    seg_size = seg_size + 1
    pos = pos + 1
  end
  if (seg_size > max_seg_size) then
    max_seg_size = seg_size
  end
end

io.write(max_seg_size, '\n')