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

local function solve(x)
  local cnt = 0
  for i = 1, n do
    if b[i] <= x then
      cnt = cnt + b[i] - a[i] + 1
    elseif a[i] <= x then
      cnt = cnt + x - a[i] + 1
    end
  end
  if cnt <= k - 1 then
    return false
  else
    return true
  end
end
local min, max = 0, 1000000000
while 1 < max - min do
  local mid = mfl((max + min) / 2)
  if solve(mid) then
    max = mid
  else
    min = mid
  end
end
print(max)