local n, k = io.read("*n", "*n")
local x, a = {}, {}
for i = 1, n do
  x[i] = 0LL + io.read("*n")
end
for i = 1, n do
  a[i] = 0LL + io.read("*n")
end

local tasks = {k}
local l, r = k, k
while 0 < #tasks do
  local idx = tasks[#tasks]
  table.remove(tasks)
  for ir = r + 1, n do
    if x[ir] <= x[idx] + a[idx] then
      table.insert(tasks, ir)
    else
      r = ir - 1
      break
    end
  end
  for il = l - 1, 1, -1 do
    if x[idx] - a[idx] <= x[il] then
      table.insert(tasks, il)
    else
      l = il + 1
      break
    end
  end
end
print(r - l + 1)