let split c s = (
    let res = ref [] in
    let i = ref 0 in
    let n = String.length s in
    while !i < n do
      let j = !i in
      while !i < n && s.[!i] <> c do i := !i + 1 done;
      res := String.sub s j (!i - j) :: !res;
      i := !i + 1;
    done;
    List.rev !res
  );;

let rec range a b = if a > b then [] else a :: range (a + 1) b;;
let read_ints () = read_line () |> split ' ' |> List.map int_of_string;;

let rec gcd x y = if y = 0 then x else gcd y (x mod y);;
let lcm x y = x / gcd x y * y;;

let [a; b; c; d] = read_ints ();;
let a = a - 1;;

let f x c d = x - x / c - x / d + x / lcm c d;;

print_int (f b c d - f a c d);;
print_newline ();;
