defmodule Main do
    def solve(l, l, _) do
        1
    end
    def solve(l, r, m) when (r - l) >= m do
        m
    end
    def solve(l, r, m) do
        a = rem(l, m)
        b = rem(r, m)
        cond do
            b >= a -> (b - a + 1)
            true -> (m - a) + b + 1
        end
    end

    def main do
        [l, r, m] = IO.gets("") |> String.trim |> String.split |> Enum.map(&String.to_integer/1)
        solve(l, r, m) |> IO.puts
    end
end