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# (.NET Core 3.1.201) (judge verdict: Accepted)

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

class Program
{
    static void Main(string[] args)
    {
        var ABCD = ReadLine().Split(' ').Select(s => long.Parse(s)).ToArray();
        var (A, B, C, D) = (ABCD[0], ABCD[1], ABCD[2], ABCD[3]);

        if (C > D)
            (C, D) = (D, C);

        var Lcm = GcdLcm.Lcm(C, D);

        var ACO = MathExt.DivideAndRoundUp(A, C);
        var ACX = A - ACO;
        var ADO = MathExt.DivideAndRoundUp(A, D);
        var ALcmO = MathExt.DivideAndRoundUp(A, Lcm);
        var ACDX = ACX - ADO + ALcmO;

        var BCO = MathExt.DivideAndRoundUp(B + 1, C);
        var BCX = B + 1 - BCO;
        var BDO = MathExt.DivideAndRoundUp(B + 1, D);
        var BLcmO = MathExt.DivideAndRoundUp(B + 1, Lcm);
        var BCDX = BCX - BDO + BLcmO;

        var ans = BCDX - ACDX;

        WriteLine(ans);
    }
}
static class GcdLcm
{
    public static long Gcd(long a, long b) => (b != 0) ? Gcd(b, a % b) : a;
    public static long Lcm(long a, long b) => a / Gcd(a, b) * b;
}
static class MathExt
{
    public static int DivideAndRoundUp(int x, int y) => (x + y - 1) / y; // (int)Math.Ceiling((double)x / (double)y);
    public static long DivideAndRoundUp(long x, long y) => (x + y - 1) / y;
}