local mmi, mma = math.min, math.max
local mfl, mce = math.floor, math.ceil
local a, b, s = io.read("*n", "*n", "*n")
local ret = 0LL
for w = 1, s do
  local hlim = mfl(s / w)
  if w <= a then
    local x = a - w + 1LL
    local ymin = mma(1, b - hlim + 1)
    local ymax = b
    local ysum = (ymax - ymin + 1LL) * (ymin + ymax) / 2LL
    ret = ret + ysum * x
  end
end
ret = tostring(ret):gsub("LL", "")
print(ret)