Problem:
Score : 300 points

Problem Statement

You are given four integers A, B, C, and D. Find the number of integers between A and B (inclusive) that can be evenly divided by neither C nor D.

Constraints

1\leq A\leq B\leq 10^{18}

1\leq C,D\leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

A B C D

Output

Print the number of integers between A and B (inclusive) that can be evenly divided by neither C nor D.

Sample Input 1

4 9 2 3

Sample Output 1

2

5 and 7 satisfy the condition.

Sample Input 2

10 40 6 8

Sample Output 2

23

Sample Input 3

314159265358979323 846264338327950288 419716939 937510582

Sample Output 3

532105071133627368

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Linq;
using System.Collections.Generic;
using static System.Console;

class Solver {
    Scanner sc = new Scanner();

    public void Solve() {
        var A = sc.nextLong();
        var B = sc.nextLong();
        var C = sc.nextInt();
        var D = sc.nextInt();

        var c = (B / C) - ((A - 1) / C);
        var d = (B / D) - ((A - 1) / D);
        var lcm = Lcm(C, D);
        var cnt = (B / lcm) - ((A - 1) / lcm);
        WriteLine((B-A+1) - (c + d - cnt));
    }

    public long Lcm(long a, long b) {
        return a * b / Gcd(a, b);
    }

    public long Gcd(long a, long b) {
        if (a < b)
            return Gcd(b, a);
        while (b != 0) {
            var tmp = a % b;
            a = b;
            b = tmp;
        }
        return a;
    }
}

class Combination {
    static int mod = 1000000007;

    public static long Calc(int a, int b) {
        if (b > a - b) return Calc(a, a - b);

        long ansMul = 1;
        long ansDiv = 1;
        for (int i = 0; i < b; i++) {
            ansMul *= (a - i);
            ansDiv *= (i + 1);
            ansMul %= mod;
            ansDiv %= mod;
        }
        return ansMul * ModPow(ansDiv, mod - 2) % mod;
    }

    private static long ModPow(long a, int p) {
        if (p == 0) return 1;
        if (p % 2 == 0) {
            long half = ModPow(a, p / 2);
            return half * half % mod;
        } else {
            return a * ModPow(a, p - 1) % mod;
        }
    }
}

class Scanner {
    string[] s;
    int i;

    char[] cs = new char[] { ' ' };

    public Scanner() {
        s = new string[0];
        i = 0;
    }

    public string next() {
        if (i < s.Length) return s[i++];
        string st = Console.ReadLine();
        while (st == "") st = Console.ReadLine();
        s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
        if (s.Length == 0) return next();
        i = 0;
        return s[i++];
    }

    public int nextInt() {
        return int.Parse(next());
    }
    public int[] ArrayInt(int N, int add = 0) {
        int[] Array = new int[N];
        for (int i = 0; i < N; i++) {
            Array[i] = nextInt() + add;
        }
        return Array;
    }

    public long nextLong() {
        return long.Parse(next());
    }

    public long[] ArrayLong(int N, long add = 0) {
        long[] Array = new long[N];
        for (int i = 0; i < N; i++) {
            Array[i] = nextLong() + add;
        }
        return Array;
    }

    public double nextDouble() {
        return double.Parse(next());
    }

    public double[] ArrayDouble(int N, double add = 0) {
        double[] Array = new double[N];
        for (int i = 0; i < N; i++) {
            Array[i] = nextDouble() + add;
        }
        return Array;
    }
}

class Program {
    static void Main(string[] args) {
        Solver s = new Solver();
        s.Solve();
    }
}