local mmi, mma = math.min, math.max
local mfl = math.floor

local function comp(a, b)
  return a < b
end

local function lower_bound(ary, x)
  local num = #ary
  if num == 0 then return 1 end
  if not comp(ary[1], x) then return 1 end
  if comp(ary[num], x) then return num + 1 end
  local min, max = 1, num
  while 1 < max - min do
    local mid = mfl((min + max) / 2)
    if comp(ary[mid], x) then
      min = mid
    else
      max = mid
    end
  end
  return max
end

local n, m, q = io.read("*n", "*n", "*n")
local dp1, dp2 = {}, {}
local t = {}
for i = 1, n do
  t[i] = {}
end
for i = 1, q do
  local a, b = io.read("*n", "*n")
  table.insert(t[a], b)
end
for i = 1, n do
  table.sort(t[i])
end
for i = 1, n do
  local src = i % 2 == 1 and dp1 or dp2
  local dst = i % 2 == 1 and dp2 or dp1
  for j = 1, i - 1 do
    dst[j] = src[j]
  end
  dst[i] = n + 1
  for j = i - 1, 1, -1 do
    if src[j] <= n then
      local lb = lower_bound(t[i], src[j] + 1)
      if lb <= #t[i] then
        dst[j + 1] = mmi(dst[j + 1], t[i][lb])
      end
    end
  end
  if 0 < #t[i] then
    dst[1] = mmi(dst[1], t[i][1])
  end
end
local tbl = n % 2 == 1 and dp2 or dp1
for i = n, 1, -1 do
  if tbl[i] <= n then print(i) os.exit() end
end
print(0)