local n, k = io.read("*n")

local edge = {}
local deg = {}
for i = 1, n do
  deg[i] = 0
  edge[i] = {}
end

for i = 2, n do
  local rem = i - 1 - deg[i]
  for j = n, i + 1, -1 do
    if deg[j] < j - 1 then
      table.insert(edge[i], j)
      deg[i] = deg[i] + 1
      deg[j] = deg[j] + 1
      rem = rem - 1
    end
    if rem == 0 then break end
  end
end
local m = 0
for i = 1, n do
  m = m + #edge[i]
end
print(m)
for i = 1, n do
  for j = 1, #edge[i] do
    print(i .. " " .. edge[i][j])
  end
end