a, b, s = read_line.split.map(&.to_i64)
ans = 0i64
prev = 0i64
sum = 0i64
a.downto(1i64) do |i|
  h = s // i
  while prev < h && prev < b
    prev += 1
    sum += b - prev + 1
  end
  ans += sum * (a - i + 1)
end
puts ans