import java.io.*;
import java.util.StringTokenizer;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));

        long a = in.nextLong();
        long b = in.nextLong();
        int c = in.nextInt();
        int d = in.nextInt();

        long divCTop = b / c;
        long divCBot = (a - 1) / c;
        long divC = divCTop - divCBot;

        long divDTop = b / d;
        long divDBot = (a - 1) / d;
        long divD = divDTop - divDBot;

        long temp = LCM(c, d);
        long divCDTop = b / (temp);
        long divCDBot = (a - 1) / (temp);
        long divCD = divCDTop - divCDBot;

        out.println(b - a + 1 - (divC + divD - divCD));
        out.close();
    }

    static long GCD(long a, long b) {
        if (b == 0) return a;
        return GCD(b, a % b);
    }

    static long LCM(long a, long b) {
        return a * b / GCD(a, b);
    }

    static class Scanner {
        StringTokenizer st;
        BufferedReader br;

        public Scanner(InputStream s) {
            br = new BufferedReader(new InputStreamReader(s));
        }

        public Scanner(String s) {
            try {
                br = new BufferedReader(new FileReader(s));
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
        }

        public String next() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public double nextDouble() {
            return Double.parseDouble(next());
        }

        public int[] nextIntArray(int n) {
            int[] arr = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextInt();
            }
            return arr;
        }

        public double[] nextDoubleArray(int n) {
            double[] arr = new double[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextDouble();
            }
            return arr;
        }

        public long[] nextLongArray(int n) {
            long[] arr = new long[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextLong();
            }
            return arr;
        }

        public char[] nextCharArray(int n) {
            char[] arr = nextLine().trim().replaceAll("\\s", "").toCharArray();
            return arr;
        }

        public String[] nextStringArray(int n) {
            String[] arr = new String[n];
            for (int i = 0; i < n; i++) {
                arr[i] = next();
            }
            return arr;
        }
    }
}


Measured memory_bytes: 21204