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 ffi = require("ffi")
local C = ffi.C
ffi.cdef[[
long long atoll(const char*);
]]

local function lltonumber(str)
  return C.atoll(str)
end

local n, m, c = io.read():match("(%d+) (%d+) (%d+)")
n = tonumber(n)
m = tonumber(m)
c = lltonumber(c)

local a, b = {}, {}
for i = 1, n do
  a[i] = 1LL * io.read("*n")
end
for i = 1, m do
  b[i] = 1LL * io.read("*n")
end
table.sort(b)
local cnt = 0
for i = 1, n do
  local dst = 1LL + c / a[i]
  local lb = lower_bound(b, dst)
  cnt = cnt + m + 1 - lb
end
print(cnt / n / m)